Tutorial on how to set up OpenWRT to let network traffic flow through ProtonVPN only for specific [list of] devices, while the rest goes through the regular routing.

There are different posts in the openWRT forum, but no one of them is specific for a private VPN vendor for this specific feature.

An example of post where after many iterations nothing really works is this one: https://forum.openwrt.org/t/any-beginners-guides-for-policy-based-routing-with-commercial-vpn-and-keeping-non-vpn-wan-as-primary-routing/177423/3