And what if I have a router (like your thread, OPNsense), top-of-rack switch (10G ports) and an access-switch (1/2.5G ports). And then the ports that face end-devices are either on the access switch (that makes sense right) as well as top-level rack switch has connections towards my server machines in my rack.

So its bit more hardware then you initially though, and all devices technically support vlans. SO basically I had two questions in one:

1. What would be the best VLAN setup for my needs (I expect here some follow-up questions, back and forth)
2. How can I configurable the VLANs correctly across my various switches, such that it actually works.. So I don't accidentally lock myself out again and needed a SW reset (lol).