lk32,

QuickBooks technical support is wrong.  As long as the file is the same product version (i.e. QuickBooks Enterprise Desktop 2022 or QBE 2020), it doesn't matter what the REV version (revision) is (R3, R4 or R5, etc).  I have QBE 2022 R3_97 installed on one of my servers because R5 won't even open.  I see the splash screen flicker and then nothing. 

The users on the R3_97 QB 2022 server open files saved on a central file server.  I have another group of users who open the same files stored on that central file server using R5_143 QBE 2022 without any problems.  I even did a test where I opened a file on the R3_97 QB 2022 server in multi-user mode and then opened the same file on the R5_143 QBE 2022 server - both files open with QBE 2022, even though one file is open with an older Rev version.

Now I wouldn't be able to open a file that was upgraded to QBE 2022 on an old machine where QBE 2020 was installed - QuickBooks isn't backwards compatible in that manner.  I've seen several users ask QB support for one of the older revs for QB 2022 and they are also told, erroneously that you can't do that.  They are wrong.  One caveat is that I only use QuickBooks Enterprise Desktop so I can't confirm the same behavior on the Pro/Premier releases, but I'm sure there are others here who can.  

As for where to find the R4 to download, I can't help with that.  I usually have to manually download at least one update during a cycle (because the product won't do it by itself) and I keep most of those downloads.  You used to be able to download older revisions from Intuit but I did a quick search and couldn't find where.  Perhaps someone else can look.