Are there summoning spells level 7th, 8th or 9th ?

[Myth27]

If yes, what are they?
If not what cr creatures or cumulative xp could they summon roughly if I were to create them homebrew ?

[LudicSavant]

If yes, what are they?
If not what cr creatures or cumulative xp could they summon roughly if I were to create them homebrew ?

Conjure Celestial is 7th level. It gives you a CR4 creature (though, this was almost certainly designed specifically with the Couatl in mind, since it is the only CR 4 celestial in the MM, and a Couatl is valuable beyond its CR).

The Tasha's summons are not 8th level spells, but perform particularly well when upcast specifically to 8th level.

Gate is 9th level. It allows you to summon anyone you know the name of. No save. This has the potential to be absurdly deadly to any opponent you know the name of...

[Millstone85]

I would say that true polymorph can be considered a summoning spell of sort. One of the options lets you turn an object into any creature of CR 9 or lower. Concentrating for the full duration of 1 hour makes the transformation permanent (but beware dispel magic) and, while the creature is no longer under your control, it might remain friendly.

[MaxWilson]

If yes, what are they?
If not what cr creatures or cumulative xp could they summon roughly if I were to create them homebrew ?

Conjure Celestial (7th) looks weak on paper until you look at the stats on a CR 4 Couatl, then it's awesome.

Summon Greater Demon (4th) scales well up to 8th level (CR 9 Glabrezu with spellcasting and truesight and beefy melee attacks and an excellent action economy) in addition to other cool stuff like CR 6 Chasmes with built-in crowd control and huge auto-crits against anyone they have crowd controlled (5th level) and CR 7 Armanites with magic weapons (6th level).

True Polymorph is a good way of producing creatures to Planar Bind (Nycaloths, Bheur Hags, etc.) or potentially-friendly good-aligned monsters (Young Silver Dragons, Couatls, etc.) or targets for Magic Jar (CR 9 Gloomweavers, CR 5 Werebears, CR 8 Goliath Werebears from Rime of the Frost Maiden).

Conjure Elemental is mostly just a 5th level spell but there is at least one 9th level application: CR 9 Frost Salamanders would be worth Planar Binding. Also, if the DM lets you summon elemental myrmidons with Conjure Elemental (they might not--I wouldn't) they have built-in magic weapons, which can be helpful on summons.

The WotC adventure Rime of the Frost Maiden (2020) has a Create Magen spell which lets you create permanent Magen minions at the cost of gold and max HP reduction--but Necromancers are immune to HP reduction so for them all it costs is gold! This isn't technically summoning but it's as good as.

Off the top of my head that's all I can think of.

[Eldariel]

Summon Greater Demon (4th) scales well up to 8th level (CR 9 Glabrezu with spellcasting and truesight and beefy melee attacks and an excellent action economy)

I'd also like to highlight one particular spell: They have a casual 8th level spell in Power Word: Stun 1/day (admittedly not a spell you would probably prepare as your 8th level option but still a solid one nevertheless). So if you ever have basically anything (not immune to stun, but stun immunity is like a handful of superthings in this edition) at under 150 HP, you just stun them and kill them. No save. Yes, they'd get a save to use their Legendaries at the end of their turn but a full turn of stun is likely quite enough to finish them off. And this from a minion. Unlike in 3e, Mind Blank doesn't protect you against Power Words so immunities are hard indeed to come by.

[SharkForce]

I would say a pretty good rule of thumb is that most spells allow a single creature of CR up to the spell level, controlled for an hour.

note that demon summoning exceeds that CR, but you won't control them for an hour in the great majority of scenarios, and it doesn't exceed the CR by much, so don't go thinking that you can summon a CR 15 creature for 10 rounds as a level 7 spell or something like that.

if you want multiple weaker creatures, I would recommend you extrapolate from conjure minor elementals or conjure fey (conjure animals is generally considered exceptionally strong for its level; you might use it instead for something you want to be particularly iconic, but I wouldn't just hand something like that to anyone, it's basically a class feature for those that get it). for the most part, the designers seemed disinclined to give multiple summons above CR 2. the exception would be create undead cast as a level 9 spell, which can get you a pair of CR 3 creatures, albeit for potentially 24 hours.