Transfer of Windows Installation to new PC does not boot

I want to migrate my Windows 1809 installation with all programs to a new PC. I tried it with backups of the old PC that I restored to the new one, but the new one could never boot it. I tried AOMEI and EaseUS, I made complete system backups of all the neccessary partitions, I restored only the windows partition after I had installed a pure new 1809 on the target PC.
I then tried to repair it with bootrec commands. This failed to, I always end in error messages like "system cannot find the path".
The disk layout of both PCs is differrent: The old one has three SATA-SSDs, a small one, now unaccessable in the mini enclosure with passive cooling once was the boot device, a boot SSD and a SSD for data. Somehow I managed to boot automatically from the new bigger SSD after quite a while tinkering with bootrec, before that I had to go into the BIOS boot menu every boot.
The target PC at the moment has only one SATA-SSD, I delete all partitions on it before I start a new restore.

Indeed: Both PCs are modern UEFI boot devices with GPT partition schemes.
Of course I started with restoring all partitions that Windows needs, this is the normal procedure with modern backup software.
Yes, I tried it with a new clean install where only substituted the windows boot partition, hoping that the boot manager would accept it.
I now will start anew with your Macrium tip.

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The tip to try Macriums Fix boot on their WinPE boot stick worked in seconds!
The new PC now boots the old Windows. Some drivers are missing still, but it works.
Thanks for this advice. I should have discribed my problems much earlier as long as I get angry over those boot errors.

I have roughly two dozen Windows keys in an extra Excel file. One of them normally works. And if not, then the next "grey" keys are only an ebay click and a few bucks away.

No, I will not transfer any license as I bought the new PC in order to have redundancy. Both should be running the same stuff.
It is a little bit of an overkill, as I now have external USB clone SSDs of all our main PCs and notebooks. But of course a genuin i7-8750 PC with a NVMe boot device in a few weeks will be a real speed king in comparison.

I live long enough in Berlin that I still can remember those years before the wall came down and the Reichstag once again became the Reichstag in real. Only a few meters away on the Eastberlin side of the wall Honecker had built the "Palast der Republik" (now there stands a replica of the old Prussian Stadtschloß that did not survive WWII and could blasted finally away from Ulbricht, for which they demolished the Palast). It was famous (among other things) for its decent restaurants (for DDR standards that where quite low of course). With american friends we had the luck to eat there during the examinations of the young personal there, no arrogant waiters no ugly platters, everything was fine (and of course cheap as we came from DM-land). And had a nice view to the enormous Berlin Cathedral on the other side of Unter den Linden.