I have had little success finding a niche that is steady or has multiple available jobs posted so I explore all kinds of job categories but what I noticed the most is even after submitting proposal employers and to chat via WhatsApp at that point I'm out
Upwork is filled with scams at the moment.
In any case, you must not contact potential clients outside of Upwork (before a contract is in place) because it can lead to an account suspension.
I'd strongly suggest you go through this post - https://community.upwork.com/t5/Community-Blog/Top-Red-Flags-for-Scams-From-Community-Member-Wes-C/b...
Once hired on a contract you are able to communicate with a client however you would like. But, if you are going off-system make sure it's something like Slack where you can easily track/save messages or screenshots from just in case.
The business to customer/user interactions are much more fluid on WhatsApp. It's extremely simple to use and one of the widest growing apps. That being said, I don't ever use it. The only one I will use besides slack or email is Telegram since it's big in the crypto space.