I am a total newbie to this forum but I imagine this question will become more and more relevant given recent Congressional action in the US with regard to user privacy.
I have a Routerboard 750GL running RouterOS 6.37.1 and I am wondering if it is possible to install a commercial VPN client (e.g, Express VPN, which offers a Linux client that they claim can be installed on routers) on this piece of hardware? I would like to be able to secure my entire network rather than one device at a time.
No, it is not possible to install 3rd party software. However most of the VPN providers are using either ovpn or ipsec which can be configured on RouterOS.
No instruction for RouterOS, but you can follow the RouterOS manual for the chosen VPN type and just enter the same values in RouterOS, as the Expressvpn tutorial says