1. Launch the game with mods
2. Go to settings > other > delete achievements > type DELETE > confirm
At this point the game has cleared all your Steam profile achievements and recreated the achievements-modded.dat file
3. Switch back to normal mode
The game reads achievements.dat file (which still has your non-modded achievements) and synchronizes them with Steam. You get a million Steam notifications with "achievement unlocked".
Since modded achievements are separate I'd expect it to not delete my Steam achievements. In that case the messaging around the delete achievements option should be reworded when with mods.
Alternatively it would be not ideal but working as described if it deleted Steam achievements in both modded and non-modded files. The current behavior of deleting achievements from Steam but not from achievements.dat is likely a bug.
[Genhis][2.0.47] Delete achievements in modded game also deletes Steam achievements, but not really
Re: [Genhis][2.0.47] Delete achievements in modded game also deletes Steam achievements, but not really
Thanks for the report. For 2.0.50, I changed it so that Steam achievements wouldn't be deleted for modded games.