Hello @Daniel Lui ,
Welcome to Microsoft Q&A forum.
I noticed that this issue was reported before, this should be the related thread: Merge tools in “Resolve conflicts” not shown.
Since this issue appears again on your side, I suppose you are using a newer version of VS 2019(>16.1.5), could you please start a new thread on our Developer Community from VS > Help > Send Feedback > Report a Problem… VS Product Team will help to fix it if this issue doesn’t fix completely.
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