Former Tune Span user, upgraded to Big Sur from Mojave

I upgraded from Mac OS Mojave to Big Sur yesterday (skipped Catalina for various reasons) and now I'm in a bind. I used to use a third-party program called Tune Span to spread out my iTunes library among different external drives, putting movies, podcasts, iTunes U, and movies, and some TV shows on one 6TB external drive and most TV shows on another 6 TB drive. This was to get around space limitations offered by my default hard drive (only 2TB) and by the largest external hard drives at the time I purchased them (6TB). As far as I can tell, Tune Span just moved the files to wherever I wanted them and updates the iTunes library files to point to the new locations.

Now with Big Sur, we have different Apps for Music, TV/Movies, Podcasts, etc. For the most part, the new apps (other than Podcasts) can see my music, TV shows, and movies where they were previously spanned using, I presume, those edited iTunes media files. BUT, when I try to add new music, TV shows, or movies, they get added to my default hard drive instead of to the external hard drives. This is a problem since my default hard drive has very little space left.

What can I do to keep my existing organization structure? I checked the preferences section - I can designation one Media folder location, but I have too many TV shows and Movies to fit all of them on any one volume. Currently the media folder location is pointing to my iTunes Media on my default hard drive. Should I just uncheck "Copy files to Media folder when adding to Library" and add any new files to the right volume manually, and then add them to the TV Shows Library?

Also, should I uncheck "Keep Media folder organized"? I'm not sure what that's doing at this point. If I remember correctly, when unchecked and then checked, it tries to consolidate all of the media files into one directory wherever it is pointing. So I should probably leave it alone right?