Roku Express sees EVERY wireless network but mine

A couple of things come to mind.

First - Here's what has worked for me to re-establish my net connection. I usually have to do this on my most used Roku, a Streaming Stick+, several times a month.

• Restart your router (even if other devices have no problem finding and connecting). Sometimes that's all it takes, if not keep going.
• Restart the Roku to clear its memory via Settings > System > System restart (for Roku TV it's Settings > System > Power > System restart). Again sometimes that's all it takes, if not keep going.
• Find and connect to your network via Settings> Network > Set up connection

If that doesn't fix it, try disconnecting the power to your Roku for a few seconds.  When it comes back up, see if you then can set up the network connection.

Second - Your Roku Express (assuming it's not the recently introduced Express 4K)  is a lower end unit with single band Wi-Fi radio that only supports the 2.4 GHz band. This, and many other devices of all sorts that are 2.4 GHz only, can't even see the 5 GHz band, !et alone connect to it. If you have a dual band router with both 2.4 and 5 GHz bands, be sure the router's 2.4 GHz band is turned on.

Within the 2.4 GHz band, be sure your router is set to use channels in the 1 through 11 range as are used in North America. Some other parts of the world also support channels 12 & 13, but Rokus can't even see these channels.

There have been a number of reports lately of people who have routers supplied by their Internet Provider in which the router's 2.4 GHz band was disabled by an update to the router software. They've had to have their Internet Provider re-enable the 2.4 GHz band, or in some cases swap in a new router with 2.4 GHz support.