The reason for my comment is that Time Machine provides the only practicable way to "undo" a macOS upgrade, should you find it necessary to do that.
Every year lots of people complain they were somehow deceived into upgrading macOS 🙄 then become angry when they learn the only way to fix that mistake is to restore a TM backup they neglected to create.
Brad BN wrote:
Should I be worried? I am using an Apple 2T Timecapsule for my backup.
I have plenty of them and all they have all been working perfectly.
Confusion arose regarding Catalina's insistence upon using "backupbundle" to identify Catalina TM backups instead of "sparsebundle" that we had been accustomed to. Apple has been silent regarding that specific change, but it can be surmised it may be in preparation for some as yet to be announced TM feature. Take note of the following excerpt from Change Time Machine Configuration preferences on Mac:
"If you upgraded to macOS Catalina on a Mac that uses a Time Capsule or other network storage device as the backup destination, your existing backups are also upgraded and can be used only on macOS Catalina. New backups that are created can be used only on macOS Catalina."
... or later macOS versions, presumably.
Apple means what they say: new backups can only be used on Catalina, but so what. You wouldn't want to use Catalina backups for a Mac running Mojave anyway. You can however restore a Mojave backup, as has always been the case.
In any event the update you describe isn't Catalina, and 64 bit compliance is another story altogether. Apple implemented 64-bit hardware and software about a decade ago. If a developer neglected those requirements after all this time, clearly they're not interested in the platform. If you want to upgrade macOS for the features Catalina offers, the workaround for you is to install (or restore) Mojave on an external drive or partition, and boot from it when you need to use that legacy software.