I’ll freely admit I don’t use that thing and was under the assumption it was feature complete. Regardless, the Android and iOS clients are also open, and I’ve found absolutely no indications that there’s any blobs in the repo or the like.
From what I’ve seen, there are some blobs. At least Telegram-FOSS says:
Several proprietary parts were removed from the original Telegram client, including Google Play Services for the location services, HockeySDK for self-updates and push notifications through Google Cloud Messaging. Location sharing functionality is restored using OpenStreetMap.
Same page is where I learned you cannot register from third-party clients btw. Not nearly as big of a blow as removal of desktop registration, but still gross that you’d have to touch a partially-proprietary official app first.
