After various tries, the shape is made but not at all by following the ellipse...
I tried various odds. I ended up giving up and doing a simple removal of material and I practiced time off to soften. It's not exactly what I wanted, but more than 8 hours of struggle, it's good...
Thank you very much to everyone. I will certainly come back to you very soon because having stopped practicing Solidworks years ago, I am starting from scratch so to speak.
at gt22, possible problem related to the SW version but maybe also to the computing capacity of the PC, I'm on a laptop, I'd test on a Workstation occasionally ...
Not yet tested on a workstation with SW2019 but on the other hand test carried out on a laptop with SW2017 and there it works the first time, it's indeed very crazy this story ... maybe a well-hidden parameter... be continued...