A couple of months back YouTube had restricted the max video resolution to 480p on mobile devices. The restriction was there just to reduce the load on internet service providers.
Due to the COVID pandemic, the whole world is not doing work from home which leads to more data uses. Because of that, the load increased on internet service providers. To reduce the load the max resolution was fixed to 480p
Now the restriction has been taken off and you can watch the videos with max video resolution on your mobile devices. The restriction is no more. But there is a catch in that.
If you are connected to WiFi then you can enjoy YouTube in any resolution but if you are connected to your mobile data then for you the limit is still 480p.
On your mobile data you cant watch high resolution videos.
The restrictions has been taken of for both Android and iOS devices.