You should review the following articles:

https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/upgrading-always-on-availability-group-replica-instances?view=sql-server-ver15

https://mssqltrek.com/2020/02/12/always-on-availability-groups-rolling-upgrades/

https://sqlha.com/2019/08/15/ags-and-wsfc-os-rolling-upgrades-what-works-and-what-doesnt/

In general, the way to upgrade is the following:

1. Upgrade the secondary node to the new version
2. Failover to the upgraded secondary node
3. Now -...

Obscure objection.  If there's corruption, you can't restore using your method.  You can't restore to the middle of the rebuild process.  Rebuild is atomic -- it works or it...

[EDIT]: Looking back at this, you're correct and I stand corrected... so far in this thread, the OP hasn't stated if he has such things in play and we're...

We differ in opinion only on whether or not using the Bulk Logged or Simple Recovery Model would be a "Pyrrhic victory" victory or not.  I'm simply not willing...

It might be easier to post the plans on this site: https://www.brentozar.com/pastetheplan/

There are a couple of things you can do to affect how sp_updatestats works.  There is a parameter available that forces the statistics to be updated with the previous sampling...

Be very careful executing sp_updatestats - it uses the default sampling rate when updating statistics which may not be good enough.  It can also be a problem if you run...

From BOL:

ROWS/RANGE that limits the rows within the partition by specifying start and end points within the partition. It requires ORDER BY argument and the default value is from the start of partition...

We don't have any maintenance on DB. It is a virtual machine. I saw that a lot of indexes take a lot of space:

Everything works...

I am not sure what that maintenance task actually generates - or how it truly identifies the indexes to be rebuilt.  My guess is there is something else involved that...

I stand corrected, I'll be honest, I forgot to look at what SQL version section this was in (I'm still mostly on SQL2014, so compression of TDE is still...

Maybe this will get you started...

Declare @startDate datetime = '2020-12-21'
      , @endDate datetime = getdate();

   With t(n)
   ...

You should review the many articles on TDE and backup compression.  It seems it will only be enabled if you modify the MAXTRANSFERSIZE on the backup command.  There are also...

With apologies for my ignorance on the subject, I'm not sure what's going on because I don't actually use index maintenance plans, mostly because of the many reported horrors...

Yes - this can all be done before the 'migration'.  Actually - this is done in place of the migration since you won't be moving the old DR server.

Yes -...