Dualboot : Win10 deletes uefi-boot-entries of other installed distros (Linux) at each boot of Win10

[mikon2]

Win10 was installed first (clean install) on Disk0  (SSD, 120 GB).

Then I installed a Linux-Distro besides the Win10 partitions.

Linux installs a boot-entry into the win-efi-boot-partition, so at boot there is a Grub-Menu on the screen where I can select the OS which I want to boot.

As long as I select Linux, everything is fine. Linux does boot and at the next start (boot) of the PC the Grub-Menu appears.

But when selecting Win10 in the Grub-Menu changes that behavior.

Win10 does boot correctly.

But every reboot from then on will never ever show the Grub-Menu again, but will boot only Win10 without any options.

Since I use primarily Linux, this is a nightmare, because after each Win-10 boot, I have to use a Live-USB-Linux and reinstall the Grub into the efi-boot-partition.  It is not hard to do it, there are tutorials all over the internet (chroot method).

But imagine you have to do that every second day.

Other people experienced the same problem. I have tried all suggested "solutions" like placing the Win-Boot-Manager at top of the Boot-Order in the EFI-Bios and then deactivate it.  People claim that then Win10 will not overwrite the NVRAM at boot because it finds the Win-Boot-Entry (although it is deactivated) and "assume" that the entry in the NVRAM has not to be created again.

But this and all other solutions do not work on my HP-PC.

I did all. Even installed BIOS again using the HP-Tool for that.

So, I have the latest version of the HP-BIOS installed, but it doesn´t help.

Another "solution" proposed:  Converting the SSD-disk from GPT to MBR.

Disabling EFI-support in the BIOS and only allowing Legacy.

Hoping, that in MBR-Mode Win10 will not touch the entries in the MBR.

So I tried that.

But there is a new problem in MBR-Mode of BIOS at the installation of an OS :

The F9 at boot (where I select the boot-medium), does not show the USB-Live-Stick, thus it is impossible to install Win10 in this mbr-mode.

In order to get the USB shown in the boot-medium menu, I have to allow Efi again.

Then it shows the boot-usb-stick under efi.

But Win10 recognizes the efi-machine and the mbr-formatted SSD and there is no way to install Win10 on the MBR-disk.

I am stuck now.

I just want the Grub-Menu at Boot in order to select Win10 or my Linux-distro(s).

Did that for years on other PC´s like Dell or Fujitsu or laptops.

This problem with my HP-PC is new to me.

I bought the HP on ebay. It is old, yes. But I like it.  Never had such a fast PC and besides that, it is my first SSD.

Booting Win10 takes 7 seconds, booting LInux the same time.

It is a dream, because on non SSD-disks and older CPUs booting took between 35 seconds up to more than a minute.

I hope for help from you, if possible.

Maybe there is no solution to this.

( Other solutions like using vmware or virtualbox in Win10 or in Linux and use the other distro from within the Virtual Machine are possible, but I don´t like that solution. )

Regards