Yes sda7 is the first partition.
Finaly my recovery (external) disk worked fine.
Now i need to reinstall ubuntu but with custom partitioning: I already have 3 unused partition which i want to use as /root, /tmp and /home.
the EFI partition is also still there. Do I need to specify efi partition during the re-installation?
You need to boot in UEFI mode. I believe grub then just installs with grub-efi correctly into the efi partition if it already exists.
You do not install grub to the MBR or any place else. Does it still give the old choices which then is a bug?
For info on UEFI boot install & repair:
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