Version Switching

I had a world in version 1.21. The other day I was playing in a server in version 1.8.9, and without thinking I go to join my single player world not realizing I needed to switch versions. The whole world was gone. Stupidly I hadn't made any backups yet because I had just recently made the world but it was very disappointing to see whatever I had built and put time into was gone. I feel like this used to be a thing but don't remember, there should be a warning before you join a world that it was made in a different version. This would give people the chance to switch versions before they basically trash their whole world. This is definitely a problem for me, and I'm sure many others, because I play servers in 1.8.9, but I play my single player worlds in the newest versions.