I have asked the staff at Windscribe that it is impossible to run a VPN without root because it needs root to create an interface for the VPN.
IVPN does run as root unfortunately. I did test it, and the servers also seemed to be pretty slow for me unfortunately. But custom DoH did work perfectly.
Thanks for asking them. It’s definitely possible without root, since for instance, ProtonVPN runs not only without root, but also fully sandboxed, and works perfectly.