there's a fan-made compendium of "fixed" 5E spells:
It is licensed CC-BY; made by Omega Ankh and somanyrobots. Judging by "design notes" section, a lot of thought went into it.
I looked into all level 1 replacements and selected the ones that have original version that is available in...
I like this version. This is not a "fix" in a strict sense, but it perfectly fits as a rare modification of the spell, with different benefits and drawbacks.
Diogenes' Durable Doppelganger. This spell’s duration is 3 rounds, plus 2 rounds for each slot level above 2nd. Instead of creating...
Another spell that was sort-of-improved in 2024 version is Mirror Image. It had two major changes:
1) The "duplicate check" was moved from "when an enemy targets you" to "when an enemy hits you" - this automatically solves the problem of bad scaling (in the 2014/A5E rules Duplicate’s AC is...
Well, it's not a Dungeon issue, but I've heard of a fan created 152-page pdf named "D4: Encyclopaedia Subterranica", where almost every hex of the map was filled by a collaborative effort. I have no idea how good or useful it is, but it's a thing.