Reading an archive policy where they're shutting down. One of the reasons cited is the old archives are on software past its end of life (this is a good thing, unpatched servers are bad), but in doing so they're removing information.

This is one of those things that is why I am a relentless advocate of data first designs.

If your data is in a format that is portable in some fashion, you can't lose it when you switch app architectures.

SQL is of course first class, but it doesn't fit all uses (either because the data is not relational in some way or the people collecting/needing it are not technical experts in relational systems.)

I hate spreadsheets for this, but if you're disciplined about it, it is an acceptable compromise, just use an open format, though xlsx is very unlikely to just up and be unusable in the future.

And as always: Structured plain text files are going to be the most likely to be usable in the future.