Now that disablelocal is gone, how to stop local (internal drive) TimeMachine backups?
Keeping an external drive connected cleans up snapshots in 24 hours. There’s no real need to disable things in my experience, other than let the hourly backups run and prune.
I would also upgrade to 10.15.7 and then report if you have some specific issue once a day passes on the new system build.
With APFS on SSD I can’t measure any performance issue since copy on write is basically handled at full speed via non-blocking IO.
The old mechanism absolutely had a performance impact so strategic cases, disabling made an effect. If you are on a hard disk and APFS, you have much bigger performance problems in general with APFS than managing the snapshots.