@Legend64 

Log in to the router, go to Advanced > Wireless > Wireless Settings, and make the changes below, at the end of step 7 do the same thing on the 5G page and switch to WPA2-PSK AES there.:

@Tony In my wireless setting, it doesn't show anything regarding WPA2 or WPA3. Only can rename network name and password

@naavin You're using the Tether app I bet? You need to directly login to the router and not use the app...

@SenderName The same problem happened to me and I logged in through the router not the app.  Any. recommendations?

@terae Hello...we had the same issue today...what you need to do is go into System Preferences/Network/Advanced, then delete out all the old wireless network names you have in the list under "Preferred Networks". And delete out the CURRENT wireless name/network you are now using with the less safe security type. 

Then, re-enter your current network in the list with the more secure security type. We unplugged the router/modem afterwards just to "reset" everything. I don't know if that did anything or not but we now accomplished our goal.

Hope that works for you!