I know that TeamViewer required certain helper apps for some device manufacturers and doesn't work with others at all. It seems like there isn't a universal approach to all Android versions and flavors
iOS and recent Android versions have accessibility frameworks that can be used to control the device
Adding the ability to control the device through a remote connection while useful for a handful of legitimate purposes would also make Telegram a security risk and a prime target for scammers on mobile devices and tarnish the name of the app when stories inevitably come out talking about people getting scammed through Telegram. Imo, the majority of the public wouldnt use it and it has too much risk associated with it. I think it should be more similar to Discord's screensharing feature where it can broadcast video and eventually audio.