I have 7 different sessions in VB as I experiment. Most started with 5.4.4.1 for no specific reason other than I'd been on mainline in prior setups, so why not? Then with the folder sharing tutorial in VB and some timely info, it became clear every one of the 5.4's despite looking really fancy, did not allow folder sharing. So I decided to upgrade the kernel, since on 20.7.2 and 5.7.1 does allow folder sharing. Problem it has is Polybar only respects Picom in the systray, but not the rest of the bar. I was curious if after the upgrade I'd still have that problem.
The session had about 8 gigs free. Not enough. I increased the disk size to 25 GB. Not enough. Exactly how fat must a disk be? 13 GB free minimum it appears from my quick and dirty research, though after the upgrade much of that space can be recovered. So I'm going to go all out and increase the size to 40GB and report back. This might be worth a tutorial. Stranger things have been known to happen.

Ryzen 7 2700, 32GB Corsair Dominator 3200, MSI Armor RX-580, ASUS Crosshair Hero VII X470, Sabrent NVMe