I have a lot less green dots on my github calendar,
I do not know why.Who can help me?
Did you possibly remove an email address from your account, or delete a repository?
In general you can see possible reasons here: Why are my contributions not showing up on my profile? - GitHub Docs
I changed my default branch and then I changed it back,and that’s it.
Then there might be a caching issue. If it takes more than a few days to fix you could contact support and ask them to flush that cache.