Sorry for not beeing precise enough.
I use my own settings for the BPL / DCU etc folders, for example instead of
"C:\Users\Public\Documents\Embarcadero\Studio\18.0\Bpl"
I use "E:\Studio\18.0\Bpl" by setting BDSCOMMONDIR to "E:\Studio\18.0" in the IDE options.
This worked in all Delphi versions so far.
Just installed upates with TMS Subscription Manager and all bpl's are in the public folder on the C: drive.installed.
Maybe a bug of Delphi 10.1 Berlin ?