So I've looked all over trying to find the best method to make sure forced subtitles are used when making a backup using DVD Shrink. So much conflicting and different advice and guides!
If I select DVD Shrink to only take forced subtitles, does it actually stay forced? What is the best way to keep these forced subtitles in the backup?

Why don't you just do one chapter with a subtitle appearance and check with your software player or DVD-RW? As far as I know, you will just have to select the subtitle of the propper language. The forced entries are flagged as such and will show, even if subtitles are turned off on your player. It takes less than 10 Minutes to try it.

DVD Shrink defaults to removing the UPOs which would allow you to turn them off. When you re-author a movie, you can right-click on the title and tell Shink to display a subtitle automtically. Still your standalone might overrule those settings.

My computers so old it will probably take me an hour or two but I will give it a go, just trying it with a chapter and seeing what happens, thanks.