Thanks for the hint to look at the wiki.
Actually MC is finally working on the new PC. However the wiki didn't help much and I had some additional work to make it work.
So I copied the files from one PC to the other which took more than a day with 1.5 TB. Then I installed MC16 on the new machine. Imported the earlier saved library from the other PC. Changed the drive names as described in the wiki.
So far so good. Then I had to import a few new files. Worked OK. But then - guess what - MC imported all the old files again and after a day I had them all twice in the library. So I removed them manually.
Then I noticed that half of my files had lost the BMP analysed earlier and which where present in the old library. Also half the cover art was lost. So I had to rebuild this. And still MC is busy to reanalyse BMP for the 60,000 files that lost it. Takes another day.
So the conclusion is: If anybody from MC could wright a failsafe instruction on how to best move (a lot of) files from one PC to another would be really great and save some rework for others, that do the same.
Otherwise: MC16 is a great software and I still love it.