If you do not want to download anything at all, there are web-based services (SaaS) that offer Telegram number validation. These are generally safer because they run on the provider’s server, not your computer.
Why? Because bad actors used checkers to harvest phone numbers for spam campaigns related to crypto scams and disinformation. As a result, Telegram now implements:
Confirms if a phone number is linked to a Telegram account.
: Start by searching for "download Telegram checker" on your favorite search engine. This will yield numerous results, but be cautious of the sources.