There are none. This is pure GM homebrew territory.
Unless you are meaning Learn a Spell, but that is for your character learning a new spell that already exists in the game system. Not for composing your own designed spell from component rules.
Magical Shorthand and Spellbook Prodigy depending on how they are read, might allow someone to learn a spell they don't have a scroll/formula/tutor for. (and the second feat provides the first, plus some) It ends up allowing you to do earn an income progress to discount the learning of the spell. So if the GM considered getting a copy of the magical writing part of the cost of learning the spell. This feat lets you discount that cost, down to eventually 0gp.
I imagine if one considered/ruled that too much to put on a single feat, you could homebrew a feat (Spell Researcher) that Acts like the Inventor feat, allowing you to do Earn Income roles to count towards the cost of a scroll of the spell, to be counted as the magical writings for learning the spell. (of course, this probably shouldn't count as an actual scroll, but can stand in for that character to learn the spell)
If you are talking about creating their own spell, or researching rarer spells, that would require talking to the GM. I'd think that it would be fine to use it with uncommon spells, with the GM likely requiring some sort of in character expedition to acquire some needed information to complete it. Things like Rare, I would assume would need something like that presuming the GM chose to permit it.
Obviously any brand new invented spell would be UNIQUE and so very rare and subject entirely to the GM's approval as to if it meets balance needs and such. That simply isn't something that is part of the game baseline.
It is notable that spell variations are acquired via the Spell Trickster feats, or class features such as the Psychic Amps. So those end up not just being necessarily a different specific spell. With such specificity if you made them as simple as, learn it this way from this better scroll you take away some of it's niche, so you should likely be careful.
Granted, with spell trickster, the caster knows/prepares one version, and can cast either with that one slot. So if you did allow the Variations, it is possible that a feat such as the trickster feat could be limited to the ability to combine them as one knowledge/preparation vs taking up two slots.
I certainly agree that granting an automatic critical success for the cost of copying a spell into a copy of your spell book seems like a simple minimum option. That could still be pretty expensive to build a backup book, and makes it harder to understand how you get to copy spells into your book for free (at level up).