Monkeying around with stuff way above my pay grade and I think I found the problem. Our ISP has upgraded to 5G, and apparently we now have a 5G network connection on our router? (I didn't know this was a thing.) Exact same name as the old wireless network with "-5G" after it. So I connected to that one instead of our old wi-fi, and now the issues I was having are gone. Also, I have six times the connection speed.
Still have no idea why I couldn't connect with the old network, but here I am.
I'm in shipping and receiving, drat it!
And about two minutes after I wrote the above, my browser stopped working, AGAIN. So I haven't fixed anything, really. No idea what's going on here. My browser stops working after an hour or three, I reboot the computer, it works okay again. It stops working. Repeat.