In the Loops picker where you have optional
"If you want a different sound for the ‘b’ substyle, enter that WAV file name in the "b substyle loop" setting."

You can have Endings with:
"If you want a one shot loop for the ending, enter that WAV file name in the "Ending loop" setting.
Or an A or B Ending loop option.

I bought some loops from SessionBand and they have Holds and Stops.
So maybe there's another option you can add.

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ReaTrak Biab & Plugin in Reaper
Free Biab Chord Picker Tool