Maybe this can get you towards your quest

Declare @string varchar(160) = 'LUMBAR - FUT MEDSª, INJURED LOWER BACK LIFTING DRUG BOX'
, @position int = 1

Select len(@string) len_String,...

You have discovered why most of us dislike linked servers !

How did you declare and configure the linked server?

e.g. did you enable "collation compatible"?

Keep in mind data transfer between your...

Does this provide usable info for you ?

SELECT 
    ar.replica_server_name, 
    adc.database_name, 
    ag.name AS ag_name,
  ...

I've always advocated against inplace upgrades ( as it may leaves potholes or ports , ... open / active )

I suggest actually migrating to a new OS with the SQL...

There is no such thing as "an easy job" !

As always with AI, you'll have to validate and test this all.

Mostly no rocket science, but applied guidelines as they should.

It will get better over time ...

- outdated statistics?

- implicite conversions?

- functions in where clause?

- did you analyse the sqlplan using the free Solarwinds Plan Explorer ?

should be yourserver.yourdomain\yourinstance or yourserver.yourdomain,portnumber

Best is to file a bug for SSMS ( Help > Send Feedback > Report a Problem. )

Yes ( according to this MS art: Supported version and edition upgrades (SQL Server 2022) )

Here are some recommendations documented by MS with regards to your question: Database files and filegroups

Did you test having

ALTER DATABASE [YourDb] SET AUTO_UPDATE_STATISTICS_ASYNC ON

ref: Alter Database SET options

Be gentle with us 

#ChallengingRoadAhead

So ... nowadays still having win2003 OS with SQL2005 or worse comes into the picture 

Don't perform "in-place" upgrades!

You'll want to migrate to an new ( and supported ) OS anyway.

Request   2 OS : 1 temporary - 1 permanent target

• on the temporary, install SQL2014...