I suffered from a killer Windows update.
Currently my Lenovo laptop has two disks, a SSD with contains both Windows and Linux, a sda with other Linux (not working). So I have two /boot/efi, one for each disk. However the SSD entry does not appear anymore in the UEFI. My only choice now is between Windows and sda (not working).
I need to add a SSD entry in the UEFI. This way, I could again use Linux.
I can do that only using Windows or an external USB disk.
Any advice appreciated.
Unfortunately A Windows Update could have caused you to not see the entry in the UEFI anymore. Since you have a non working Linux on that device you can either try to repair it or do a reinstall. Either should fix your issue.
What boot-loader were you using when it was still working? I don’t dual-boot, but sounds more like you would have to live boot and then chroot into your Linux installation and then from there you would need to reinstall grub to the correct boot device and most likely something similar if you are using systemd-boot.
I used Grub and saved my partitions using Clonezilla. I thought the simpler way was to add a new UEFI entry using Windows but I failed to do so.
The isos of EndeavourOS (Mercury) and Arconet failed to install. I thought Ventoy was a reliable tool but this time I have no success.
many people unfortuantely have issue’s with Ventoy
Ventoy needs to be up to date before you can install with it. You also need to make sure you have Windows Fastboot and Secure boot Disabled. (We do not support Secure boot out of the box)
You can use Rufus to burn your ISO.
I updated VentoytoDisk to the feb. 2025 version and EndeavourOS booted live. I shall install it tonight and cross my fingers. I have some cleaning to do before.
Fastboot and Sec boot are disabled.
Sorry to register under my Linux name. I am also minimax and the problem is now solved. I only did a mistake when installing, I formatted my small /boot/efi partition which resulted in losing the windows bootloader. So, after restoring it with clonezilla, I resumed the install without a hitch, and using grub os prober, I could start again my old and faithful linux.
I must say that fortunately, on my 256G SSD, I had not only Windows but two linux (one unused). This way I did not lose anything, but the windows shot was nearly as close as for trump. 
Thanks for your precious help.
Thinking about this and what Cphusion wrote above, I think the whole matter could have been solved in 15 minutes.
Just grab an arch iso, chroot into the “lost” linux partition and regenerate grub (mkconfig…). My bad. I’ll be ready for the next time and Windows will not catch me by surprise.