Are you looking for something with a nice UI or just hardware you can install your OS on and roll everything yourself? What’s your budget?
Ubiquiti makes a pretty user-friendly rack-mounted router: https://store.ui.com/us/en/products/udm-pro
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/
If you’re just looking for a compact server that you can install your own OS on, then SuperMicro has a sale going on right now: https://store.supermicro.com/us_en/catalogsearch/result/?q=SuperServer 1u&categories=Deals
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.
Try looking in the network panel to see if any resources are failing to load? Any chance FF sync is installing extensions that are interfering?