I put Fedora on my 2012 MBP Retina. I made a USB key, iirc with the Fedora USB image tool, then plugged the USB key into the MBP and held the Option key as I powered it on. USB key shows up as a bootable option.

I have the same model and installed Ubuntu from an ISO burned to a bootable USB. It works great!

I have the 20133 2015 13". MBP, and I installed OpenSUSE Tumbleweed from a USB stick. Everything works. You might just have to install facetimehd camera driver.

I have Manjaro running on a 2013 MBA. Installed on a USB with Ventoy. Runs great.