Hi @HazmiMenexenus,
Greetings from the Roku Community!
We're glad you've reached out to us regarding this concern. It seems that you've been great at troubleshooting this issue. We're happy to assist further.
For screencasting to work, please make sure that your mobile phone is connected to the same network as your Roku device. Also, turning off devices may not ensure a successful reboot. Kindly restart your router by plugging it out to the power source for approximately 60 seconds, then plug it back in. Do the reboot with your mobile phone as well. As for your Roku device, try performing a system restart by going to Settings > System > Power > System Restart.
Furthermore, since you're using the Samsung S20 and S23, it should give you the option to do a "Smart View", For easier access, try to locate this option as well. You can also check out this support article to learn How to screen mirror your Android successfully.
We hope this helps. Let us know what you find out, and we'd be happy to help further.
Warm regards,
Janadee
Nadee K.
Roku Community Moderator