There was a change in location between some versions to the old file with favourites so it may still be accessible.
using an explorer window enter into the address bar
if you see a file called SumatraPDF-settings (SumatraPDF-settings.txt)
as per standard practice back it up before editing or other changes
You should be able to then copy the backup into the new location
it is at your own risk to overwrite the new with old so if you made changes to the new one back that up also
The settings file is volatile that means that whenever you make significant changes you should guard a copy against windows corrupting it during update cycles.
Favourites were intended as a temporary way of tracking file and page locations.
One new feature under development is to have a .vbkm file with such groupings (currently only for pdf) and that is available to experiment with in the pre-release version as right click
Highlighting is currently going through changes so no guarantee it is there in every pre-release however just testing today’s version [SumatraPDF-prerel-12417-64.exe] it is still working the old way using Ctrl and left mouse or selecting text then in either case press A for annotate the coloured block
RE: highlighting a word of caution always backup the source file e.g. master pdf before adding highlights as currently you would not be able to remove them without using an editor.
To ensure you don’t affect the file don’t use save as but if you do want to save to a new pdf with highlights then do use save as