How would U deal with UEFI compliant firmware in a "prebuilt" computer if you want to replace Ubuntu with Trisquel livemedia ?

Sorry for attaching a copy of a IRC chat I recently had on Libera.Chat but I think it's the best introduction to the problem I am having since my old self assembled P4 based computer, due to a swollen capacitor, began (among other things) damaging my storage devices.

In short:
I have been "forced" to buy a "prebuilt" UEFI compliant computer that has a 240 GB SSD with a Spanish version of Ubuntu 20.04 LTS in it. The computer is managed by an I3 processor with a BIOSTAR H410GMH motherboard and a 8 GB total memory.

I would like to continue using Trisquel as a liveUSB in it because that is the way I have been using Trisquel in these last years, But, by default, the new computer is booting into Ubuntu and I have never managed a UEFI compliant motherboard before and I don't want to mess things up.

Because I know that each motherboard manufacturer has its own UEFI-BIOS screens and that even the same manufacturer uses differen versions of the UEFI-BIOS screen I have told jxself I would upload shots of the "UEFI-BIOS" screen my new computer is using so that our conversations are all based on the same sort of screen.

In the next posts I will upload the shots of the UEFI-BIOS screen my new compñuter is currently using.

PS: When checking the attachment of this post I discovered jxself had begun answering to my irc request about 10 minutes before I discovered he was talking to me. So I also want to thank him for those 10 minutes of valuble comments.