Telegram Desktop usually accepts images from the Windows clipboard and sends them as pasted, but sometimes the only option is to send as a file (attachment ?). Why would that happen ? - more importantly, how can the normal image pasting be restored ?
I think this is a question for the Telegram support channels. Especially since this question is not Manjaro or Linux related in any way.
Problem is - I get no response from Telegram - so I searched Google and it showed a post in Manjaro about Telegram Desktop, so I also posted one.