I defined a git tool installer called "portable-git-2.28.0" to install Portable Git for Windows automatically onto Windows agents. I confirmed that the tool installer works as expected and is used when I clone with performance enhancements disabled.
When I enable performance enhancements, the repository size correctly hints that JGit should not be used. Unfortunately, instead of selecting the named git implementation that the job defines, it selects the implementation named "git".
In my case, that selection is not a serious issue, since the implementation named "git" is the default command line git installed on the agent.
I expected that it would select portable-git-2.28.0 as the git tool because that is the git tool that was defined for the job. I was assuming that if JGit is not selected, then the git tool defined in the job should be the preferred implementation.
Issue is visible in the /job/Tools/job/git-portable-for-windows/ job on my computer.