Honestly, Roman, I think for most situations, it is best if you handle this on your own. Make your own decisions about what kind of behavior you will accept, and what kind of behavior you will require a client to change in order to work with you.
A client emails you on Saturday? This is "unbearably rude" behavior. Client uses your first name instead of last name? Also rude in some places. Client Zoom calls you with paintings of unpopular British monarchs in the background? Also unbearably rude in some people's eyes.
But you can't report everything that is rude to Upwork. And even if you did, Upwork can't do anything about most rude behavior.
- Say nothing and continue to accept the client's money.
- Ask the client to change her behavior. ("I like working for you, but I would like you to stop emailing me on Saturdays.")
- Stop working for the client. ("Things have changed for me, and I can no longer work on the project after next week.")
- In RARE cases, it may be appropriate to report a client's actions to Upwork, particularly if the client has violated a SPECIFIC Upwork TOS rule.