Non-compiling commits make bisecting harder, when the goal is to find the commit that broke the build or a specific test. IMHO having to skip over non-compiling merge commits only makes bisecting take more time, and it may also "pollute" the test pipelines if all commits are going to be built. Additionally, merging and fixing the merge in separate commits makes it much hard to revert a merge later, in case it turned out that the merge introduced something unwanted).

So I will always recommend doing the merge and fixing the merge in the same commit. Ideally this produces a squash commit that can easily be reverted later when needed. This makes the merge process more time-consuming, but it can help to keep the builds more stable, and to more easily track which commit (merge) introduced a particular problem.