ORA-01623 & ORA-00312 while dropping one red log file

I got the following errors while dropping one redo log group:

Please note that our database is an RAC One Node database that I’m trying to convert to Single-Instance database based on the client requirements.
So, thread 2 (instance 2), is not there actually.

If we query about the redo log files of instance 2:

So, what we need to do to be able to drop the redo log files of instance 2, is to disable thread 2 as follows (database must be open):

alter database disable thread 2;

Niow, we can proceed with the redo log group dropping without issue:

Thanks
Ahmed