Installing Linux Ubuntu 19.10 on Asus n550jk with windows 10

I'm trying to installi Ubuntu 19.10 by following these steps:

1. I downloaded the Ubuntu iso and i created a partition by using windows disk management;
2. I created a bootable USB by using universal usb installer;
3. I rebooted my PC by using the UEFI firmware settings (maybe this is the only way to access to the BIOS with an asus laptop);
4. I ordered the boot peripherals: first USB, but the settings are not saved thus I changed three settings. (i) secure boot control: disables; (ii) fast boot: disabled; (iii) launch CSM: enabled. Now I am able to put first USB.
5. There are two USB options in the BIOS' boot: (i) [UEFI: "USB brand's name"]; (ii) ["USB brand's name"]. If I put (i) as first, nothing happens, namely windows 10 is run. If I put (ii) as first, I am able to run the Ubuntu's live version, but there are other two problems: (i) there is a message which says that on my laptop there is not an operative system (neverthless there is windows 10); (ii) when I try to install ubuntu in the free space which I allocated at point (1), this message is showed:

"The Partition table format in use on your disks normally requires you to create a separate partition for boot loader code. This partition should be marked for use as a Reserved BIOS boot area and should be at least 1MB in size..."

Online I read that this error is due to the fact that I didn't use [UEFI:...] as first choice in the BIOS' boot, but, as I said, the [UEFI:...] option does not work.

Can you help me to overcome these stressful problems please?

EDIT

Premises: (i) if secure boot is enabled, I cannot enable launch CSM; (ii) when launch CSM is enabled, there is also the option launch PSE OpROM policy.

The trials I did are the following (notations: sb=secure boot; fb=fast boot; CSM=launch CSM; PXE=launch PSE OpROM policy; e=enabled; d=disabled):

1. sb=fb=CSM: d (all options disabled); in this case, after rebooting, there is [UEFI..]. I put it as first choice in the BIOS's boot, but the result is that windows is run, not the USB.
2. sb: d and CSM: e and PXE: d; result: see (1) and morover there is the option ['USB name'] concerning the non UEFI mode.
3. sb: d and CSM=PXE: e; result: see (2).
4. sb=fb: e and CSM: d; result: see (1). These are the default settings.
5. sb: e and fb=CSM: d; result: see (1).
6. sb=fb: d and CSM: e; result: see (2).

Thank you for your time.