Hi Stan,
The mute command on Windows is Alt A. Here are a few Windows keyboard commands for Zoom pasted below. Hope this helps.
Windows available Keyboard Shortcuts
F6: Navigate among Zoom popup windows.
Ctrl+Alt+Shift: Move focus to Zoom's meeting controls
PageUp: View previous 25 video stream in gallery view
PageDown: View next 25 video stream in gallery view
Alt: Turn on/off the option Always show meeting control toolbar in Accessibility Settings
Alt+F1: Switch to active speaker view in video meeting
Alt+F2: Switch to gallery video view in video meeting
Alt+F4: Close the current window
Alt+V: Start/Stop Video
Alt+A: Mute/unmute audio
Alt+M: Mute/unmute audio for everyone except host Note: For the meeting host only
Alt+S: Launch share screen window and stop screen share Note: Will only work when meeting control toolbar has focus
Alt+Shift+S: Start/stop new screen share Note: Will only work when meeting control toolbar has focus
Alt+T: Pause or resume screen share Note: Will only work when meeting control toolbar has focus
Alt+R: Start/stop local recording
Alt+C: Start/stop cloud recording
Alt+P: Pause or resume recording
Alt+N: Switch camera
Alt+F: Enter or exit full screen
Alt+H: Display/hide In-Meeting Chat panel
Alt+U:Display/hide Participants panel
Alt+I: Open Invite window
Alt+Y: Raise/lower hand
Alt+Shift+R: Gain Remote Control
Alt+Shift+G: Stop Remote Control
Ctrl+2: Read active speaker name
Ctrl+Alt+Shift+H: Show/Hide floating meeting controls
Alt+Shift+T: Screenshot
Switch to Portrait/Landscape View: Alt+L
Ctrl+W: Close current chat session
Ctrl+Up: Go to previous chat
Ctrl+Down: Go to next chat
Ctrl+T: Jump to chat with someone
Ctrl+F: Search
Ctrl+Tab: Move to the next tab (right)
Ctrl+Shift+Tab: Move to the previous tab (left)