I'm in the same boat as you. There was something about integrating SM, but I couldn't get it to work. There are two decent open source choices IMO.

Meld Merge (https://meldmerge.org/) is my favourite, due to being cross-platform. Works well for merging, and `git difftool -d`. Although I cannot get it to run decently on macOS nowadays :(

WinMerge (https://winmerge.org/) is also good, but Windows only.