When I try to delete or edit a node in my realtime database, I always get the info that I have to select a key with lesser elements to change something, else it is in read-o
You're mixing three things here:
Your database console switched to read-only mode, which happens when you have a certain amount of data under it.
The warning is badly translated. Please file a bug report for that.
The database console doesn't handle clicks correctly anymore. I already reported that internally last week, and added your report to it. This bug has been fixed internally and will go into production by May 23.