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.
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.