We can assume that shy of hardware problems / your phone really reaching end of life, it's unlikely anything has changed with the phone. I would use that as the starting point, logically, if this were my problem.
- I would look at your router, if it is stable, and if it needs updates.
- I would also turn off newer WIFI technologies / options on your router if you can, 1 at a time, to see if you can find a fix.
I had problems getting my bike computer to connect to our home wifi. After struggling quite a bit and very little fruitful research, I figured out that it is because our home router was combining the 2.4 and 5.0 ghz channels into one SSID and depending on the device to use a newer wifi technology to sort this out, which my bike computer could not do. I turned the router combined SSIDs option off and now we have two separate channels and you have to choose which to connect to and/or enter passwords for both if you want access to both. This was the fix that my bike computer needed. It also had the benefit of making my connection for my laptop stable in the furthest room from the router. Previously the laptop would presumably try to use 5.0ghz but that doesn't pass through stone walls as well and then would become unstable. Now that I can force it to 2.4ghz it works happily in the furthest room.
I know that's not exactly the problem you're having but I mention it in terms of interoperability of newer and older wifi devices...
Good luck.