This about Play Services and not the Play Store. Play Services are a bunch of extra APIs/services that Google does not make available as part of AOSP. The non-nefarious reason is to make it possible to fix bugs and roll out features faster because the OEMs are terrible at rolling out new Android versions. The possible nefarious reason is to make more of Android closed-source.

At any rate, microG is a reimplementation of Play Services.

You can directly download the Telegram APK from: https://telegram.org/android

(Or using the app store that is part of /e/OS and serves as a front for both the Play Store and F-Droid.)

you can't download telegram from telegram.org?

Telegram is a Russian spy app, it needs remote attestation you are not a bot because collecting bot data is not valuable.

Telegram works on my /e/OS device. I am using Obtainium to download it, but you can also download it from the website: https://telegram.org/android