I don’t think iOS allows multiple VPNs to be enabled simultaneously. There appears to be only one VPN on/off toggle switch. From what I’ve seen you can have different vpn profiles but only enable one at a time. I could be wrong though.

Desktop operating systems like macOS, Linux (did I mention yet that I use arch Linux?), BSD, and um… that other one… oh yeah, Windows do allow this. I’m sure there are a variety of compatibility problems, but in general, multiple VPNs with the same or even different technologies can work together.