Thanks for the feedback/guidance.
I found another way to get this done, and was curious what the community thinks about this (as some may find this a hack).
I have my openhab running on a raspberry pi (with openhabian). This openhab instance connects to my “private cloud server” and Alexa doesn’t work with this instance in its current form.
I installed a second instance of openhab in a docker image on the same raspberry pi (this doesn’t have to be in a docker or on the same raspberry pi; can be on any hardware in the same network). The 2nd instance is configured the exact same way as the first instance (from items, things point of view) with the difference that the second instance connects to the standard openhab cloud.
The things, items files are the same on both instances. I removed the sitemaps and rules from the 2nd instance. This second instance of openhab is in principle my interface to Alexa and it works just fine.
The first instance is connected my private cloud server and used to manage the sitemap, etc.
My home is mostly using MQTT based HW/switches/lights/pool/audiosystem, philips hue and wemo. All those continue to work fine with this dual setup.