After also getting frustrated with the built-in WiFi of the Tesla Gateway box occasionally disconnecting (usually when I'm out-of-town, of course), I just recently installed this product:
It's a little WiFi to Ethernet bridge powered by USB. You'll also need a female-to-female RJ-45 (Ethernet) coupler and an Ethernet cable to run into the Tesla Gateway box. (I figured it was better to set this device
outside the metal box of the Tesla Gateway.)
By the way, has anybody else never had cellular support with their gateway? My Powerwalls were installed in March of 2020 and I've read that the 3G cellular was going away, but I've never seen that work as a fallback when its WiFi support lost connection (or my internet service went down).