True Polymorph Retain Class Solution

[Grondsmash]

The phrase "It retains its alignment and personality." should include your class level, subclass, feats and life experiences, as these are what has formed your alignment and personality. To not have them sounds pretty stupid, but there are really petty people who DM and rule on such stuff. They want you to act like that person, without any of the things that made you that person. Pretty weird logic they want you to believe.

The line from the Polymorphs of "The creature is limited in the actions it can perform by the nature of its new form, and it can’t speak, cast spells, or take any other action that requires hands or speech unless its new form is capable of such actions." Does imply you can use your former abilities if the new form can speak and move properly to cast spells.

There is a semi-simple solution for this, the 5th level Modify Memory spell. Best to prep a written list of Class/Sub-class, their abilities, your highest level of spell ability & highest level and number of spell slots, list of feats and any relevant choices (like fire for Elemental Adept), list of major events you were part of and list of friends, enemies and significant acquaintances you know. The spell specifically says “…its mind fills in any gaps in the details of your description.” So, have a friend cast it, read off the list, hold the spell for 1 minute, and all those things are recalled, your mind fills in the gaps (not hard as you lived them), and "POOF!" you are restored.

For qualifying for the spell, the 6 second event of you having all those memories, changing into a new physical form and losing all your memories, at the time of casting qualifies as the event, if you cast this spell after the initial hour (so it is permanent) but before 24 hours expires, it will be within 24 hours and they will "allow the target to recall the event (the losing of their memories and abilities in 6 seconds) with perfect clarity and exacting detail" while “its mind fills in any gaps in the details of your description.” Easy to get all the exact details since this is the mind and personality that originally held them!

All that being said, you would lose any racial ability or race-required-feat, as you are now longer of that race. And unless you have a really generous DM, which I doubt, as your current DM is forcing you to use this solution, rather than just being a decent sort and having them with the True Polymorph spell, you will not get those abilities nor feats back. Count them as lost and no replacement feat or ASI, for example.

[RSP]

The line from the Polymorphs of "The creature is limited in the actions it can perform by the nature of its new form, and it can’t speak, cast spells, or take any other action that requires hands or speech unless its new form is capable of such actions." Does imply you can use your former abilities if the new form can speak and move properly to cast spells.

It doesn’t imply that, at least as I read it.

[The creature is limited in the actions it can perform by the nature of its new form],

and

[it can’t speak, cast spells, or take any other action that requires hands or speech unless its new form is capable of such actions.]

The new form can’t do the listed things, unless its new form is capable of such actions means, to me, that those abilities need to come from the new form.

[JackPhoenix]

The phrase "It retains its alignment and personality." should include your class level, subclass, feats and life experiences, as these are what has formed your alignment and personality. To not have them sounds pretty stupid, but there are really petty people who DM and rule on such stuff. They want you to act like that person, without any of the things that made you that person. Pretty weird logic they want you to believe.
Alignment and personality are its own thing on the character sheet. They have nothing to do with class level or any other stats.

The line from the Polymorphs of "The creature is limited in the actions it can perform by the nature of its new form, and it can’t speak, cast spells, or take any other action that requires hands or speech unless its new form is capable of such actions." Does imply you can use your former abilities if the new form can speak and move properly to cast spells.
No, it does not.

There is a semi-simple solution for this, the 5th level Modify Memory spell. Best to prep a written list of Class/Sub-class, their abilities, your highest level of spell ability & highest level and number of spell slots, list of feats and any relevant choices (like fire for Elemental Adept), list of major events you were part of and list of friends, enemies and significant acquaintances you know. The spell specifically says “…its mind fills in any gaps in the details of your description.” So, have a friend cast it, read off the list, hold the spell for 1 minute, and all those things are recalled, your mind fills in the gaps (not hard as you lived them), and "POOF!" you are restored.
That's not how Modify Memory works.

For qualifying for the spell, the 6 second event of you having all those memories, changing into a new physical form and losing all your memories, at the time of casting qualifies as the event, if you cast this spell after the initial hour (so it is permanent) but before 24 hours expires, it will be within 24 hours and they will "allow the target to recall the event (the losing of their memories and abilities in 6 seconds) with perfect clarity and exacting detail" while “its mind fills in any gaps in the details of your description.” Easy to get all the exact details since this is the mind and personality that originally held them!
You're correct you'll remember the moment losing those memories. That does not help you regain anything the spell replaced..

All that being said, you would lose any racial ability or race-required-feat, as you are now longer of that race.
The first any only (partially) correct claim in the entire post. You lose your racial abilities along with everything else except personality and alignment, as the spell says.

[KorvinStarmast]

Alignment and personality are its own thing on the character sheet. They have nothing to do with class level or any other stats.

No, it does not.

That's not how Modify Memory works.

You're correct you'll remember the moment losing those memories. That does not help you regain anything the spell replaced..

The first any only (partially) correct claim in the entire post. You lose your racial abilities along with everything else except personality and alignment, as the spell says. The OP seems to be be thinking about how Shapechange retains class abilities.

[JackPhoenix]

The OP seems to be be thinking about how Shapechange retains class abilities.

In which case, there's nothing to solve, because the spell does that by default.

[Chronos]

Class levels and personality are completely different things. Does your sense of humor change when you become better at casting spells? Do you become more introverted or extroverted when you get better at swordplay? Do improvements in your stealth skills change your bond, or your character flaws?