feat: download multiple channel at once (bulk download)

Hello.
i ve used yout application and successfully donwloaded a history of a channel. Want to send you a cup of coffee.
i am not a programmer.

When iniating the process, the application asked to enter file extension separated by commas.
i ve entered Html, gussing it could give the output of the chat history in Html format, like the Actual Telegram desktop applciation does.

I ve found that the output is in Json format.

-Question: Could you clarify what exactly the application step "enter file extension separated by commas" does?
-Question: will it be possible to download multiple channels, meaning bulk download, or at least one by one without entering a cahnnel number each time? instead enter all the numbers at once and await the sequencial download?
-Question: is there a way to have the output chat history in html page readable format similar like it is done in Telegram deskop app?