TeX Live and MacTeX ⇒ Package update/migration Mac2015 to Win10 TeX Live 2021

[Molemi]

Dear Fellow TEXs!

I am assisting a colleague who needs to migrate from an older Mac (ca. 2015, never updated) to a current Win10/TEX Live 2021 installation.

After successful installation of TEX Live 2021 I tried to process LaTEX files that have been productive on the old system, but get so many issues of missing packages, TEX live does not cope and breaks down with numerous "?".

I have successfully produced a list of packages installed on the old system, but see no way to import this into tlmgr.
My idea has been to try to import the package list into tlmgr and have the manager decide which of the (in some cases obsolete) packages needs to be replaced.

The package list is over 3000 lines strong, so going through one by one does not seem feasable to me.

Thanks for your suggestions!
:-J