I'm in the same case as you, I bought it many years ago and now ... development stopped, MacOs version even became read-only, and for a few days now, it even stopped to work!
They try to force us to move to boxcryptor 2 which are, in my point of view less features and an awful subscription model. I really need to use multiple encrypted folder as multiple and distinct virtual folders.
I had a looked at your proposition "Viivo", I didn't know about it but I wasn't really happy about what I can read on their own website, so I dig a little bit and found https://cryptomator.org
It's open source, available on Windows, Mac and Linux, no registration or whatever. I've just installed it and it seems pretty good so far, I found back my virtual disks matching some folders, the possibility to mount -or not- some folders, etc ... And it has filename encryption.
You should give it a try, I'll update this post if I found any bad behavior.