I recently obtained a Dell t620 that I've rack mounted, and I'm using to upgradey homelab. I'm also thinking I should upgrade my routernsince I'm having to reconfigure a lot with the new server(I have a 12 year old Netgear wireless router).
Forgot to mention that before I got the R210 II, I had a Ubiquiti Unifi USG-PRO-4. It worked okay but the hardware is pretty low end. You get a nice pretty UI and many more options/configuration compared to a consumer router, but it's hamstrung compared to what you can do with OPNsense/pfSense IMO.
I ended up finding an old 5 GB sophos router that I was able to flash pfSense onto, it's not rack mounted, but was way cheaper than spending $500 on a ubiquiti.. I like it so far, but need to do more testing
You can also check out pfSense, which is an OS that does routing and more. You can install it on your own hardware or buy a machine through them:
https://www.pfsense.org/products/
Just know that whatever you pick to replace the router-portion of your current Netgear device, you'll also have to invest in a separate WiFi access point to provide your wireless network.
If you don't mind the drama, both PFsense and OPNsense are perfectly competent router OSes.
Regarding hardware:
OPNsense also sells rack-mountable server hosts.
OP may not actually need a rack-mounted server -- I have several machines just sitting on a 2u rack-mounted shelf. My opnsense install runs on a cheap protectli box, and there's enough room for a handful of raspberry pis and their power bricks on the shelf next to it.
IMHO, it'll use less power than a server, plus, it's about the right amount of processing power for a router / firewall (I use pfSense, but there are other router solutions out there)
You won't want to virtualise / containerise that function, so anything more powerfull can be kept in a separate device.