I'm looking for a website or program that would look at your past games on Lichess or chess.com and find moves that you played that were blunders and create puzzles around those
I don't know of a single program that does all that. I do it myself with following steps. I save most of my games in a pgn file. The interesting ones, esp. my losses, are analyzed by Stockfish. The "blunder threshold" is your choice, typically 3 - 5 pawns or more. With Notepad++ text editor I enter the FEN of the position in a pgn file, of course preceded by the tag line [SetUp "1"]. Answer is best line of Stockfish. I skip positions that are cooked by good alternative choices. When 50 - 100 puzzle positions are accumulated I transfer the pgn file to my Android phone & tablet. I display them with iChess but many other apps handle pgn files.
Lichess has the "learn from your mistakes" feature, which can be used to play your significantly bad moves in a game as a puzzle.
From your profile, select a variant/time control on the left, then click "view the games" in the top right. Click on a game, go to the analysis board, and at the bottom, in the "computer analysis" tab, click "request a computer analysis". Once you've done that, a button will appear on the bottom right for you to "learn from your mistakes".
With a free account you're limited to a few analyses a day, (I think it's around 30), and this is a bit of a manual process, but it's relatively close to what you have in mind. Also, unless you're on really short time controls, (for which puzzle rush would be better training than learn from your mistakes), you're not likely completing more than 30 games a day, so you can catch up with yourself at some point.
I found this reddit post which has two comments which answer this question.
This is essentially exactly what I was looking for and bonus points in that I think I found their github that has their code which seems shockingly simple
I made something like that, both open source http://chesstacticsgenerator.vitomd.com/ Description: Generate chess tactics from your own lichess games. This is based in the info that lichess generates (blunders, mistakes) https://github.com/vitogit/pgn-tactics-generator Description: Generate chess puzzles / tactics from a pgn file (this uses a python library & stockfish to evaluate blunders)
(Note, I am not affiliated with any of the links / software / repositories)
Lichess generates puzzles from your games automatically.