From different installations of git I seem to have two different shells: MingW64 (fromGitGUI) and MSYS.
In R Studio, the menu item git -> shell invokes MSYS, but I'd prefer the MingW64 shell.
It seems to work using the menu Tools>Global Options, then in the tab "Terminal", "new terminal opens with", and either it's there, or you can set "custom" and indicate the path.