I'm confused by your question. F5 is a method to open the Bar Settings Dialog Window and Utility Tracks are not included in the Bar Settings Dialog Window, only the 8 original Legacy Tracks. I don't understand how you're attempting to mute from that dialog window.

Beyond that, are you asking to mute the entire track or to mute and return to normal (unmute) regions of a Utility Track?

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F5 - Bar Settings Dialog Window for BIAB 2022 Windows version

BIAB 2025:RB 2025, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.