I downloaded the correct version of the Joomla 3.9.22-8 osx stack.
The first try to start this resulted in the error-message that the program couldn't find a required Mac-address.
Thereafter I wanted to try the program with its own default Joomla-website, so I deleted the .bitnami folder with all of its contents (after having stored a backup of it in a safe place). When I started the stack again all went well. The window of the program appeared without error messages and I could start the default Joomla application.
My idea is now that, when I could find the location where the default website is installed (such as htdocs), I might be able to transfer the latest backup of my website there en restore it with help of Akeeba's Kickstart.
My main question is now: would this be a feasible procedure, or should I proceed otherwise?
When the answer to this question would be 'yes' then I"ll have some additional questions (f.i. where tot find the correct directory for restoring my website; and: is the MariaDB-database in the new stack compatible with the MySQL-database of my original website?).