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I got a fatal error and I'm thinking about reinstalling it. Do my game files stay? I mean I have like 9-10 different game projects and I don't want to lose my work. Can anyone help?
Yeah, your yyp files stay wherever they are. If you do a completely fresh reinstall as per the instructions, they will no longer show up in recent projects, though, so you'll have to find them wherever you saved them
Though this would only be if you're getting crashes within minutes of launch dozens of times per day. Occasionally GMS2 just normally crashes for me every couple weeks.
Given the fact you're asking this question: Please look into version control software! make an account at github.com and store your projects there. Easy to do refactoring / testing, reverting to backups (as well as keeping an off-site backup), and checking back changes that you made.