How do I respond to clients wanting to chat on email/ telegram or whatsapp instead of on the Upwork platform?
Just send them this link and tell them you'll be happy to use any of the options Upwork allows for you initial discussions:
If they agree, make sure they know you can communicate however they wish once an Upwork contract is in place.
If they don't agree, cease contact with them. You don't want to do business with people who don't play by the rules.
Too many clients know little and care less about how Upwork works.
Dismissing a potential client out of hand is foolish. If such a client pays no attention to the information you provide them regarding how Upwork requires you to communicate with them, Liesl-Ann, report them to Upwork by flagging their job posting.
Otherwise, hope for a fruitful bit of work with them.