Some issues with UEFI on Dell Inspiron 14 3481

Hi,
I've in my hands a laptop on which I'm trying to install Slackware -current via usb, but I'm encountering some problems with UEFI.

The laptop is a Dell Inspiron 14 3000 (model 3481) originally shipped with Ubuntu 18.04:

• CPU: i3-7020U 7th gen
• RAM: 4GB
• Storage: 1 TB 2.5" HDD

There is the possibility to switch to legacy mode only for external media.
This allowed me to start the installation procedure from usb.

I've recreated a GPT table from scratch and added three partitions:

• EFI (code EF00): 100M
• Swap: 4G
• Root: the remaining space

When I start the installation, the EFI partition seems to be not recognized by the installer and at the end of the setup, if I skip LILO installation, it does not show me anything about ELILO.
When finished, after rebooting the system, the laptop doesn't find anything to boot.

I've also created an usb stick for boot, as suggested by Pat in the README_UEFI.TXT.
This allowed me to boot the system after reswitching from legacy to UEFI, if I remember correctly. That was the only time I was able to run Slackware.

What am I missing?
Thank you in advance for your time.

Cristiano.