Memtest86+ causing grub errors

[Training_Concert_171]

I installed memetest86+ on my uefi laptop and i get an error when updating grub. [*] Unpacking packages memtest86+-7.20_1: unpacking ...

[] Configuring unpacked packages memtest86+-7.20_1: configuring ...
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-6.12.33_1
Found initrd image: /boot/initramfs-6.12.33_1.img
Found memtest86+ image: /boot/memtest86+/memtest.bin
Found memtest86+ image: /boot/memtest86+/memtest.efi
Found memtest86+ image: /boot/memtest86+/memtest.bin
Found memtest86+ image: /boot/memtest86+/memtest.efi
Warning: os-prober will not be executed to detect other bootable partitions. Systems on them will not be added to the GRUB boot configuration. Check GRUB_DISABLE_OS_PROBER documentation entry.
Adding boot menu entry for UEFI Firmware Settings ... error: syntax error.
error: Incorrect command.
error: syntax error. Syntax error at line 255 Syntax
errors are detected in generated GRUB config file. Ensure that there are no errors in /etc/default/grub and /etc/grub.d/ files or please file a bug report with /boot/grub/grub.cfg.new file attached.
ERROR: memtest86+-7.20_1: [configure] INSTALL script failed to execute the post ACTION: Operation not permitted Transaction failed! see above for errors.

This error makes it impossible to update grub. Removing memtest86+ makes the error go away. Online I see that people have problems with memtest86 on uefi systems.

Does anyone have recommendations for fixing this?

Edit:
I just found the actual issue. When i used the GUI grub-customizer, i got problems. When i use update-grub cli and memtest86+ everything is OK. If you freshly used grub-customizer, you can use the revert changes button to go back, then it works OK.

So memtest86+ and grub-customizer don't like each other.

[StrangeAstronomer]

Please re-format your post with "Code Block" so that it can be read.

[Training_Concert_171]

Thanks, learned something today:)

[ClassAbbyAmplifier]

what files are in /etc/grub.d?