Bard Magic Secret Help

[Khrysaes]

I assume this is no,

but the bard's magical secrets says

"A spell you choose must be of a level you can cast"

And a bard that is multiclassed with a full caster, say a sorcerer,

"You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes,"

So a 1 sorcerer/9 bard has 5th level spell slots available.

but if I understand it correctly, they can't choose a 6th level spell for their 10th level magical secrets even if they have 6th level spells available?

[diplomancer]

You're correct, they can't get a 6th level spell.

Relevant rules:
"You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class. "
"If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slots, but only to cast your lower-level spells."