Possible cause:
Router updates from some internet providers lately have turned the 2.4 GHz band of dual band routers off, just leaving the 5 GHz band.
Your Express+ has a single band wifi and can only use the 2.4 GHz wifi band on channels 1-11. It cannot even see the 5 GHz band, let alone connect to it.
If that proves to be the problem you'll want to have your 2.4 GHz band turned back on. If you can't do that yourself you may need to have your internet provider do it.
If you have other wifi-equipped devices (phone, tablet, smart tv, etc), if they can tell you what wifi band and channel they are connecting to it might help diagnose the problem.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X