First of all note that:

There is 9 digit old chat ids and 10 digit new chat ids.

There is two internal links for it:

Android:

tg://openmessage?user_id=1234567890

IOS:

tg://user?id=1234567890

And a web link for telegram web:

https://web.telegram.org/k/#1234567890

When you click on this web link it redirects to username if its available:

https://web.telegram.org/k/#@USERNAME

And there is a username link for windows:

tg://resolve?domain=USERNAME

This one doesn't have an "@"

Combine these and build your solution.