After upgrading TRS22 and Plus, you need to initiate the DBR. There's a bug, which manifested itself since SP4, where the initial DBR doesn't start after upgrading. The only way to initiate this DBR is to start Trainz. You can see this operation running by choosing show logs under the developer menu. I believe, don't quote me on this, that this issue has been fixed.
This initial DBR can take a VERY LONG TIME followed by a lengthy caching (pre-caching). In total, my DBR ran for 14 hours plus another 22-hours for precaching content.
Once this is done, you can then go into Content Manager and update content. Yes, there are a lot of updates including packaged content that needs to be brought up-to-date. There are some known faulty packaged that can't be updated due to the conflict in Russia and Ukraine where the authors are located. Other than those packages, everything else is fine. Out of the 1.1 TB of data, the only faulty assets I have are the known ones mentioned.