git gui crashes on startup on Big Sur, "macOS 11 or later required !"

[jogu]

git gui crashes since upgrading to macOS Big Sur, after outputting "macOS 11 or later required !"

The Wish binary is aborting, the call stack is:

2   libsystem_c.dylib             	0x00007fff20296720 abort + 120
3   Tcl                           	0x00007fff6fe14b55 Tcl_PanicVA + 398
4   Tcl                           	0x00007fff6fe14bd5 Tcl_Panic + 128
5   Tk                            	0x00007fff6ff14ad5 TkpInit + 385
6   Tk                            	0x00007fff6fe94788 0x7fff6fe63000 + 202632
7   Wish                          	0x000000010be07582 0x10be05000 + 9602
8   Tk                            	0x00007fff6fe86a2b Tk_MainEx + 1201
9   Wish                          	0x000000010be0755a 0x10be05000 + 9562
10  libdyld.dylib                 	0x00007fff2035e621 start + 1

(full crashlog here: https://gist.github.com/jogu/708792a63754efc724015c6598b855e4 )

I'm running https://sourceforge.net/projects/git-osx-installer/files/git-2.27.0-intel-universal-mavericks.dmg/download

I tried uninstalling & reinstalling but it didn't help and couldn't find anything helpful by googling. Any hints at how to fix it would be greatly appreciated!