Bad news first: Free tools are currently out of the question
The good news: Yes, there is a way to make this work!
What do you need?
UHD Copy from DVDfab... a $49 app. Available for macOS and Windows
How does it work?
it's pretty straight forward.
UHD Copy will select the playlist of the main feature, which you can change in case it picked the wrong one or you want to remux something else.
deselect/select audio and subtitle streams you want to keep
You can add external Subtitles (tested with SRT), which will transformed into PGS
change the Font, Font size, etc. - You can't change the placement, e.g. within the picture on widescreen movies
Batch export is also possible
Set output folder and hit Start
That's it
Final remux was tested with a Oppo UDP 203 on a NTFS & ExFAT HDD connected via USB. The Oppo was connected to a Dolby Vision capable TV.
Dolby Vision and Dolby Atmos are recognised.