With many games certain things get baked into a save so if you remove a mod which provided some info in the save then the game will not like it and the game or the save will not load. Depends on the game and depends on the type of mod but uninstalling a mod mid-game is generally not recommended.
Larian is not doing anyone any favours with the hotfixes and patches not just breaking mods but breaking some peoples games (even if they don't have mods). This means that troubleshooting is made more difficult and that those who don't now anything about modding are in even deeper water than they need be.
One could always try something that's really out there like using a search engine.
This is the second hit on the DDG page below and is dated 8th of August, i.e. 5 days after game release.
How to Fix “Failed to load the main menu from the current game mod” in Baldur’s Gate 3
https://www.followchain.org/failed-to-load-the-main-menu-baldurs-gate-3/https://duckduckgo.com/?q=FAILED+TO...=1&start=1&atb=v185-1&ia=webFuckin' rocket surgery.
