CTE or subquery only, or use the expression instead of the alias
Easiest, tbh, would be

CASE datepart(month,DATEOFBIRTH)
WHEN 1 THEN 'Yes'
WHEN 2 THEN 'No'
ELSE...

Don't shrink. The free space will be used for future inserts, future new tables, etc.

Only time I'd shrink is if more than half of the DB is empty...

My thoughts are as I posted earlier.

CheckDB before backup. No point in taking the backup if the DB is damaged or hardware is failing

Probably related to the new cardinality estimator.

Identify the queries that have degraded in performance, tune them or add the hint to force the legacy CE.

As Paul said, don't ever configure 1 file for 1 core by default. Read that blog post, it's still pretty much what's recommended.

If it's a demo environment, can you get a copy of the DB from elsewhere? Or recreate it from source?
You can repair, but the problem is that it  doesn't...

Corruption is (generally) the IO subsystem mangling the data file.
It's not going to then go and write a structurally correct log record that describes that corruption that can then...

Please don't post multiple threads for the same problem.

No replies here please. replies to  https://www.sqlservercentral.com/Forums/1979641/SQL-Server-detected-a-logical-consistencybased-IO-error

Got a clean backup? (backup before the corruption occurred)?

Is the database with an ID of 9 (according to sys.databases) named SL_AppDemo?