Telegram Foss clients exist only because of unpaid volunteers that take Telegrams messy mix of open and closed parts and rip closed parts out and replace them. The Telegram organisation is notoriously late to release the source code to their current release. If they do, its a giant squashed commit without proper changelog. These releases must then be first wrangled by volunteers to be well buildable.

The Telegram Org itself gives no support to volunteers at all.

You can't register with Foss builds. Only official binaries. Nowadays a lot of features are premium only. You can only get premium with official binaries. That part is closed.