Telegram

Telegram is a cloud-based desktop and mobile messaging app developed by Telegram Messenger LLP. The app was initially released in August 2013.
One of the main features of Telegram app is cloud-based messaging. This feature allows the users to access their account from multiple devices. Users can share photos, videos, audios and other files individually or to a group of up to 100,000 members. The app also allows the users to delete or edit the messages from both sides.
Another important feature of Telegram app is secret texting, the messages are sent with the client to client encryption in so-called secret chats.

The major flaw of this app was custom-designed encryption protocol instead of end-to-end encryption which is more reliable and secure.

Telegram X

In 2017, Telegram Messenger LLP launched another app called Telegram X with higher speed, sticker animations, themes and more efficient battery use. Apparently, they bought an alternative client called "Chellegram" which they acquired and turned into Telegram X. Although the app works same as the previous one but has some different function and changes in it.

Telegram VS Telegram X

Telegram X has a slightly different home user interface when compared to the regular Telegram app. Telegram X has a call option in the menu, while on Telegram chats and calls are separated by tabs, like Whatsapp. Telegram X also feels faster than the regular Telegram app due to its fluid animations.
Unlike Telegram, Telegram X has a night mode which could be enabled via the menu and it works very well with OLED screen, but you can change the theme to dark to get a similar effect on the regular app

Night mode in Telegram X
Another feature of telegraph X is saved messages tab that makes it easier to locate your saved files. On the regular app, you are forced to tap on the Saved Messages icon then tap on the drop-down menu to access the tabs, which is a little bit complicated.
Telegram X also features an Advanced Mode which includes a lot of new features.

The advanced mode in Telegram X
The regular Telegram app used way more data than Telegram X. Telegram X has added the Data Saver feature. It saves data when you switch to mobile data and roaming.
Another major difference between both apps is gestures. Telegram X has gestures while the regular telegram app had not. For example the ability to forward messages by sliding the message to the right. This feature allows you to send the message to others by holding your finger on it and sliding the message to the right. In this version, you can also slide your finger to the right or left on the home screen to enter the chat or call page.
If we compare the features of both messengers Telegram X is way better than Telegram. Different people have different requirements so they will judge something based on their requirement. So, merely because Telegram has more users does not probably mean it is better.

Above Picture Source: https://superfamilyprotector.com/blog/en/telegram-x-vs-telegram-compare/