What model do you have? Does it support any open source firmware such as DD-WRT, OpenWrt, or FreshTomato?

TIL Google makes routers.

Go to the local thrift store, look at their routers, search the openwrt and fresh tomato support databases for them.

Pick the one with the features and speeds you want that’s supported by either openwrt or freshtomato.

If you would like to go on a different route, a mini PC with opnsense is also a good choice. If you happen to have a small form factor PC somewhere that can be added a nic card to have at least 2 Ethernet ports, this would totally work

It absolutely does matter. The obvious privacy aspect is that it's the base of your entire network so it can gobble up all your data. The security aspect is that routers based on OpenWRT get security updates for many many years, unlike typical routers.

You can usually find halfway decent routers people are getting rid of for like $10 bucks that support openwrt. Just make sure its compatible.

You could go for a used GL iNet Router. They have a nice GUI for openWRT. At this point I would mistrust everything Google made

Apart from open WRT, there's also opensense or opn Sense which let's you turn any old computer into a router as long as it has 2 network cards.

You may also need a switch and a WiFi AP tho, so at that point you better get an openWRT router. Just leaving this info here in case it's useful.

I recently bought a Brume 2 from Gl.Inet, on sale I think it cost me 60€, it runs openWRT and works really well. It has the added bonus of providing a built-in wireguard server (and also client) so I can easily access my home network from anywhere.

If you can spare 130€ the Brume 3 is now out and quite a bit better.

You can always put them in AP only mode and get a dedicated router running your OS of choice. If your internet speeds suck then anything made in the last 10 years should be plenty. But if you’ve got a gigabit connection and lots of simultaneous connections you may need to find something that’s not bottom of the barrel.

Good news is that gigabit internet has been relatively common for 10+ years so you can find old high end devices for the same price as old shitty ones. WiFi AC routers are basically worthless at this point so finding a nice one cheap isnt an issue. And if you’re using the newer nicer google ones for WiFi then the fact it’s an old slower standard doesn’t matter.