You have 28 days left before notifications stop working, thanks, Telegram.

Here is some explanation:

Your notification is delivered to your phone with FCM(Firebase Cloud Messaging), by the Telegram server sending notification with API Key coresponded to the App.
We third-party App developers are using the App configuration page on my.telegram.org to configure the API Key for our client.
However, the old FCM API was deprecated last year and will be removed soon, and Telegram still hasn't updated its configuration page(which received no update for 10 years) to reflect the API changes.

In the latest Telegram Android, the Telegram server may request the client to do a Play Integrity check at any time with error code INTEGRITY_CHECK_CLASSIC_X, then the client will perform a Play Integrity check and resend the request with the invokeWithGooglePlayIntegrity method.

TLDR: Telegram can check whether you are using genuine Telegram app on a "genuine" Android device at any time while you are using the app.

well...great news, they updated it!

However, the account associated with the API ID of Nekogram was banned 4 years ago and I do not own the phone number anymore.
So there would be an API ID change for Nekogram, you have to log out and re-login to complete the change to receive push notifications.

Q: Download/Upload speed is unstable, fluctuating between fast and slow.
A: Telegram is throttling your upload and download requests server-side(speed limiting), this is not a bug. Turning off Download speed boost may give you a constant speed(but slow of course), or pay for Telegram Premium.

Try out the free voice-to-text conversion with Whisper* for non-premium users, provided by Cloudflare Workers AI.
Configure your Cloudflare credentials here first.

*It might provide better results than Telegram one.