A lot of reasonably competent geeks just never get deep into networking, and VPNs can be overwhelming. It doesn't really help that for a long time it was all IPSec which basically you need to learn voodoo to manage. Thankfully we have much better tools now, but it's still just a tech layer that many people don't touch frequently.
The tailscale client should have created an interface, but I've never used it on a box also running wg. You don't have a tailscale specific interface in ip addr show at all? That's.... odd.
Relay "ams" means you're using tailscales DERP node in amsterdam, this is expected if you don't have direct connectivity through your firewall. Since you opened the ports that's unusual and worth looking into, but I'd worry about that after you get basic connectivity.
So to confirm your behavior, you can tailscale ping each other fine and tailscale ping to the internal network. You cannot however ping from the OS to the remote internal network?
Have you checked your routing tables to make sure the tailscale client added the route properly?
Also have you checked your firewall rules? If you're using ipfw or something, try just turning off iptables briefly and see if that lets you ping through.
I use this to run an instance of Hyperion on the tv to run leds on the back of it, that dynamically change color to match the show. Since it's native on the tv it works in jellyfin or my pc hdmi cable.
For me running jellyfin in the tv works so well, it's worth giving it network access.
Just turn off swap? You don't really need it, and the kernel wiil just oom kill without it.