@Tony, Many thanks for your supportive reply, but: I found the 'elevate/leapp' method on this almalinux-site: "https://wiki.almalinux.org/elevate/ELevate-quickstart-guide.html";
On that site is explicitely stated: "This guide contains steps on how to upgrade CentOS 7 to RHEL8 derivatives such as AlmaLinux, EuroLinux, CentOS Stream, Oracle, and Rocky Linux. You need CentOS 7 system installed to use this guide.". I used the steps of just this site, resulting in the blocking described earlier. I took the method for a valid one.. An alternative would be using the "almalinux-deploy.sh" script, but that is applicable only for transitions Centos 8 > Almalinux 8, and -sad enough- I don't get how to upgrade my Centos 7.9 to Centos 8, despite the method using multiple 'sed'-files, being hinted to on the github site offering the deploy script. "https://github.com/AlmaLinux/almalinux-deploy"; The steps described for using these sed-commands (only one? which? all?) simply are too big for me. So I am blocked on 2 levels now... oldisnotnice
