Strange UEFI installation

[Radvan]

My old HD has gone. They gave me a SSD disc, some Samsung. It is NVMe most likely. The Debian 10 netinst CD does not know it in Legacy mode so that I had to switch to UEFI. Now, strange things started to happen.
(1) If I select "Advanced options" -> "Expert install", the installer does not find the disk, even in UEFI mode. It shows a short menu with "verify CD" and so on but with no disk related options.
(2) If I select "Install" , the installation runs. It seems to run OK to the end. Then the comp is rebooted and crashes with "Operating system not found". The end.
(3) Nevertheless, if I start the comp and invoke the boot menu (F12), and select "UEFI boot" -> "Debian", the installed Debian is found and runs.
(4) If I shut down the runnig Debian and then power on the comp again, I get "Operating system not found" again. I have to reboot and click on F12 until I get boot menu. Then select UEFI Debian.
(5) I also tried rescatux (0.73). It does not find the disk.

What should I do? I would like to get rid of the boot menu every time I start my comp. I would like to understand the nonsense above a bit. Any ideas?

It is Dell Inspiron 7720 (i7) so that the BIOS settings are rather none. The netinst ISO was Debian 10.6 .

[Radvan]

Answering myself: I need to switch off not only Secure boot but also Legacy ROM suppert. Debian now starts without need to select it from the F12 menu.

Q: After switching off Legacy boot support in BIOS settings (F2), all boot options (CD, etc.) vanished. Survived only UEFI Debian and UEFI Network. Does it mean that I have to reenable the support before booting from a CD? For example, my Debian has crashed seriously for some reason and I need to reinstall...

[Edit] New feature has been discovered: Now, I cannot suspend the comp. Once suspended, the comp never wakes up. I have to powe off and power on. Is it possible to enable suspending now?

[Head_on_a_Stick]

I need to switch off not only Secure boot

Debian buster supports Secure Boot but some UEFI implementations require that the loader is marked as "trusted" from the firmware ("BIOS") menu.