Roku, Alexa and older computer no longer able to connect wirelessly

Older computer was unable to connect to internet. Tech came and set WPA to 2 which fixed that problem but newer computer could not connect. Per troubleshooting person online at Xfinity, modem is able to provide wireless for both WPA2 and WPA3 devices and went through process recommended. Now, older computer cannot connect to internet and all three Rokus (one Roku tv, two Roku devices) and even newer Alexa devices can no longer connect although all show that there is a strong wireless signal from our home network. What is the actual fix to allow devices that are five or more years old to connect