Deep-linking is not working in Web K.
I have my own bot. And I generate link for users to connect, like that:
My browser (Chrome 93.0.4577.63) ask whether to open it with desktop or Web version. I choose web version.
Then Web K opens and I've got "Start" button to connect to the bot.
And when I click on it in my bot I recieve only "/start" message.
If I choose to open with desktop version instead, I recieve "/start 123456789" message
Telegram Web 0.7.2 K, Chrome 93