I accidentally removed SELECT permission from my user on SQL Server
Checking all the items in Membership means you are adding yourself to all the roles defined in the database. That includes the sp_denydatareader role, which is probably the main reason you cannot open the Properties box any more.

If you have been given the permission to alter roles previously, it is likely that you have not removed it by your erroneous actions. So, you could just try to remove yourself from the sp_denydatareader role by executing this command in a query window:

ALTER ROLE sp_denydatareader DROP MEMBER your_user_name;


If that succeeds, you can then try opening the Properties box again and undoing your mistakes.