Something came to mind, but there are two items in question.

1) Does "backup the current preferences" saves all of the settings? or it misses some? If it saves ALL the settings, than there is a fairly easy solution to my request.

Automate installation of the new version to create "backup preferences" before installing itself and generate name of that file to include the version number of current version. Example: v728_backup_date

2)Does "downgrade" gets rid of all changes made by "new" patch or it leaves code? If "downgrade" gets rid of new code then it is a matter of looking up "backup preference" file to figure what version you had, downloading this particular version, installing it and loading preference file.

A single button "go back to previous version" would be ideal, but I do get how it can get tricky, so the above solve and semi-automate the process.

Videotrack, If user updates BIAB with every new released patch, then it is easy, you just go back to "previous" patch. Without looking/cheating I do not even know the number of the current ver. For now, I will keep 728 until 2021 version released, just because it is stable. I spent many hours trying to figure out issues with some builds and even Andrew could not figure it out based on crash logs, etc.. until I got lucky with version that stopped acting up (728).

So to put it in the right perspective, it should benefit both, users and PG crew. For example, somebody who had version 723 jumps to version 730, forgetting (or not paying attention) to the version that they had prior to that. 730 goes bananas on them. They contact tech support / forum and saga starts...
Assuming that version 723 worked for that person, it would be logical to
suggest to install 727(24,25,26,28, 29) to pinpoint if issues related to specific patch, instead of trying to figure out bugs blindly and as in my case (and a couple of others I seen) fruitlessly. What I suggested above will at least give the last working version number that person had installed that could be resurrected with ease.