chat button missing

Welcome to the Zoom Community, @dimyaz.

Without knowing a lot more about the specific situations, I'm thinking that in the meeting where you did not see the Chat button, the Chat was disabled.  Sometimes buttons that should appear in the main menu bar are moved over into the "More" button's sub-menu.  Always check there for any missing buttons.

"I'm thinking that in the meeting where you did not see the Chat button, the Chat was disabled" - 

If I go to the same meeting, but from the phone, then the chat is available there.

Also, I reinstalled the app on my PC, but it didn't help.

Also I don't see "More" button in my app.

PC

Mobile: