Can't Install SSMS 18 with Visual Studio 2019
Installing SSMS 18 GA will fail if Visual Studio 2019 has been installed, as the former requires Visual Studio Tools for Applications 2017, which will not install if the latter is already installed.
Great. Thank for letting me know.
I’m going to close it.
Justin Trout commented
It seems this is resolved with SSMS 18.1, which seems it may be related to the issue with a space in the path. Although VSTA 2017 (standalone) will not install with VS 2019 already installed, so it may have been something related to that.
TL;DR, try 18.1.