When updating MacTEX installation using tlmgr, an error occurred about siunits package (https://ctan.org/pkg/siunits). This package was declared present but could not be found.
It was impossible to delete this package with "sudo tlmgr remove -force siunits" because the package was not found !
The solution has been to delete the collection where this package was present:
sudo tlmgr remove -force collection-mathscience
And then install it again:
sudo tlmgr install collection-mathscience
Now you can update MacTEX without error:
sudo /usr/local/texlive/2021/bin/universal-darwin/tlmgr update --self --all
