Google still supports Google Play Services with security updates, and many of their apps and services are still updated via on-the-fly updates (non-app updates).
You can use the latest Youtube app compatible, it will most likely work. If not, just use the browser for it. Version 16.40.36 from October 16, 2021 is the latest one compatible with Android 5
Firefox still supports Android 5, and is the minimum requirement.
You can use AirDroid to mirror the screen of your phone to a desktop computer. Minimum requirement for it is Android 4.4
I used a Android 2.3.7 device for 2 weeks 6 months ago that goes to the internet using Via Browser, had GPS using a 2014 version of Maps still working to this day, old videogames still installed and called and sent SMSs just fine. You’ll be fine.