In pfSense you can select stateless connections for specific rules - example of stateless NTP below:
If I were you - I’d try setting up pfsense on a spare machine just to try it out - I’ve never had an issue setting it up on bare metal, virtual machine may be different…
Looks like DrayTek has a router matrix that shows session capabilities of their routers:
https://www.draytek.com/products/router-matrix
DrayTek 3912 Series looks to allow the most sessions (1000k)
Couldn’t find this information for Fritz Box or MikroTik