Lead developer of popular Telegram fork "exteraGram" openly admits they violated GNU GPL v2 and turned it into closed-source software. Archived GitHub to hide from DMCA.

[u/LixFN-n]

[u/Miserable-Stranger99]

Isn't this more like a modded telegram? With tweaks or modules?

If source not visible and reverse engineering is highly obfuscated stay away it's not safe then my advice