Hello Damien
During my research on the Internet, I came across the blog of a Swiss photographer who recommends a photo printing company (https://www.whitewall.com) on his blog. I was able to order the photos there as you recommend in your instructions (6500K, no correction) and have already received them.
I then calibrated the EIZO CS2740 monitor with the Spyder X according to your instructions. This worked very well and the result is almost perfect. The photos look a bit different in my workroom than on the screen, but that's probably because my ceiling light is +/- 5000K. I can live with that.
I've already read the first 5 modules of the Raw Class for the first time and made notes on them, applied some of them to my photos and today I'm printing out the WB sheet, then I'll continue.
Thank you for your help!