I had 2 machines force upgrade me. A MacBook Pro and a Mac Pro 2019. In both cases, I don’t recall what I did to trigger it.
I didn’t get any notification on either Mac, but I did get a handful of restarts and progress bars before Sonoma came up.
To roll back my MacBook, I had to format the drive and install Ventura using Internet recovery. Since it was a clone of my desktop I connected it with a Thunderbolt cable and used Migration assistant since that was much faster that using the backup on my NAS.