Every time starting Rust steam is checking the data files....

Well, gets anoying. Even after the game closed for no reason,
the next start i have to wait 5 minutes until all files are checked.
How to fix that, or is that a common thing now?

It’s set to do this if you’re crashing. Are you crashing?

in steam library…
right click on RUST…
click “properties”
click “local files” tab
click “verify integrity of game cache”

if that does not fix it…
follow above…
last step click “delete local content”
and reinstall.