Thanks for your quick response but unfortunately the page doesn’t want to open.
I hopefully found a solution to my issue.
During a long time I worked with my internal hard drive for my pictures and videos and one day I didn’t have place enough on my iMac, so I decided to buy a NAS to store my files on it and also to start my iMac on an external 4 To SSD, less expensive than to buy a new iMac, but one day I had an issue and My iMac didn’t’ want to start anymore.
In fact I decided to reinstall Mac OS X high Sierra on my genuine internal hard drive but No more Lightroom and photoshop update and version was available for OS X 10.13.6 High Sierra.
The solution is the following:
I can run Lightroom and photoshop CC2020 from my external hard drive on my internal one without issue and also without taking any space on my iMac. For me it’s the only solution I found instead to buy Studio Mac which is to much expensive for me.
I don’t know if I explained myself correctly but it works now