Some MacOS stuff.
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First, the term working tree refers to the current checked out branch, the working directory in it's present state.
It is recommended that comparison are made on commited, clean states, and not on uncommited changes. To compare with the current uncommited state of the working tree move the changes to staged. If not, new files won't show up at the SEARCH & COMPARE dialog, but this is tricky.
Use the VSC Git extension. To evaluate if a stalled branch is worth to be maintained, check out the develop, master, or main branch. If not very sure of the result, create a merge test branch.
Right click on the stalled branch and select Compare with Working Tree. The SEARCH & COMPARE section will read Compating XXX to Working Tree, being XXX the right clicked branch. The interpretation of the output is based on the changes to be done to XXX to reach the state of WT. Therefore: