Thank you for your reply.
As I said in my original post, using FUSE - as you suggest - was my initial setup which raised the question mentioned in the last line of my post. I admit it is very basic; yet, I would be grateful for an answer to it.
Due to your recent answer to the post https://community.cryptomator.org/t/automatic-mount-monitor-script-for-macos/2329/2 of tobihagemann, I realise that the above-mentioned High Sierra unmount bug is fixed in Mojave. At the present stage, I would still prefer a smaller scale solution as upgrading the OS might have undesired side effects.