Is Mobiwol incompatible with WiFi networks, e.g. my home network?
The incompatibility of wi-fi and wi-fi tethering is due to the way most "no root firewalls" work. 


  Sometimes this depends on the Android version in question because some
  Android versions have a bug preventing tethering and the VPN service
  working together.


Some devices hibernate Wi-Fi, preventing tethering from working when the screen is off and this behaviour can be disabled in the advanced Wi-Fi settings.

Currently as it stands, it seems Mobiwol firewall still has no compatibility with wi-fi or wifi-tethering in which case I would recommend installing an alternative no root firewall e.g NetGuard.

Netguard has confirmed support for wifi-tethering as mentioned here:


  Can I tether / use Wi-Fi calling while using NetGuard?
  
  Yes, but this needs to be enabled in NetGuard's settings. Whether or
  not it works depends on your Android version because some Android
  versions have a bug preventing tethering and the VPN service working
  together.


You could also browse Izzy's F-droid repo with similar firewalls here: Internet firewalls and choose the one suiting your needs.

Reference


NetGuard: FAQs