Convert Musescore 4 files to Musecore 3

I am a long time user of Musescore and I love it. I have made hundreds of scores and I use it daily.
I also love new features BUT Musescore 4 is slow and laggy on my laptop and I need to go back to Musescore 3 but now all the files I opened in Musescore 4 and saved are not compatible with Musescore 3! How can I get around this???