if you want to try to export your stuff...
...purely as a backup plan!
I used this code (a few weeks ago) to export our 1700+ membership info in 100-count JSON files (you might be able to go bigger, I didn't try):
Note: I didn't use the actual chrome extension, I looked at the code and went directly to the export URL to get the json exports. I think you'll see what I mean if you download the zip and look at the code -- and like, I'm on my phone now but I probably have some stuff still on my laptop I could share, if there's any interest.
Note: I didn't try the companion script to download messages.
Note: To be clear, we used the groups.io transfer service and were very happy with it -- I only downloaded our membership data as a "just in case" backup plan.