I can't explain why the Open Profile Directory button doesn't work. Sounds like an OS issue to me, but be that as it may...

I don't know Pop OS, but in Linux Mint, the default location of the Thunderbird Profiles is </home/(your user home dir.)/.thunderbird/>. In Ubuntu, which installs apps as Snaps, the Profiles are </home/(your user home dir.)/snap/thunderbird/common/.thunderbird> So you can use your file browser and look there for your missing folder file. It should be somewhere in the <Mail/Local Folders> sub-folder of your profile, but if you moved it it could be elsewhere. If you have a file search utility, you could search for the file itself, which should have the name you originally gave it.

Also, when you use Thunderbird's search feature, if it finds something, it tells you its location. If the search results window doesn't show that column header, you can add it by right-clicking on the column headers row. See attached image.

Thunderbird on my laptop is a flatpak installation, which might be why the profile location is not listed on the Troubleshoot page. Unfortunately flatpak is not as completely integrated into the OS like debian installs, but was preinstalled with the OS and not my choice. After hunting around, I found the profile under "Home/.var/app/org.Mozilla.Thunderbird/.thunderbird". I did not find my "Business" folder in the collection of other mail folders. However, I did a search as you suggested and it was listed under another mail folder. When I checked Thunderbird, it seems I had inadvertently moused the folder into another one as a sub-folder. So, I simply drag-and-dropped it back to its proper location. When I originally checked for that possibility I missed it for some reason. Dummy me. The message that probably originally told me that came and went so quickly that I couldn't read it. Thanks for your help!