Experiencing same problem (as Doomdeer) on MacBook Pro 5,1 “Core 2 Duo” 2.4 15" (Unibody, Late 2008).
Will try installing from an older EndeavourOS iso, and then upgrading, and report back.
Just ran into the same problem as OP on a MacBook Air 13" Mid-2012 (model A1466), with both Cassini 22_12 and Cassini Nova 03-2023_R1.
Artemis Nova 22_9 boots fine, but online install kept failing with pacman errors. Finally tried offline install which did work, and was able to upgrade to newest package versions after rebooting into the installed system.
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That is great to hear. 
Sorry, I forgot to report back! The offline install of Artemis-22_6 was successful. Then I was able to upgrade to most recent version without a hitch.
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I report here 8 months later, my budgie installation corrupted after updating, so tried to reinstall… same issue on Cassini Nova, It hasnt been fixed… 
cant even boot to the installer. The best solution is to get artemis nova iso, install no enviroment, and just get the latest enviroment with terminal. Sad.
Ventoy still works if you choose the option below Normal.
I can’t even boot on the USB.
Getting the same error as before with regular Cassini
Are you using Ventoy?
Ok I didnt know what you meant by that… So I did some research… WOW Ventoy is such an amazing tool. I am gonna use that and add a bunch of linux isos to my USB… I-ll let you know how it worked.
Also for the record… I couldnt install from Artemis Nova iso anymore. I keep getting “cant run pacman” error on calamares. Probably cause of outdated keyrings. So that trick doesnt work anymore. Will try with Ventoy.
OK Ventoy worked with grub2 mode. I think that’s what it’s recommended to install the latest Endeavour OS. If anyone has the same mac book pro I have (5,3) insert it on the USB slot that’s farther from you. On the first one, it kept hanging on me. Probably had a bad connection cause I had a wide USB mouse connected on the side and the uSB drive was also kind of THICC.
Remember to boot in Grub2 mode.