Help - Sequoia installer USB not showing up on late 2013 iMac

I have a late 2013 27" imac which was running Sonoma with OCLP on an external NVMe without a problem. I accidentally clicked "upgrade to Tahoe" like an idiot and it stopped working so I formatted both the internal and external disks and did a clean Catalina install on the internal HDD.

tl;dr : I tried installing sequoia with OCLP, but when I arrive at the step where I need to reboot to select the installer, it doesn't show up (I only get two options : the HDD and the EFI partition with an HDD+OCLP logo which only contains the HDD with Catalina). Any idea how to solve this ?

Here's the detail of what I am doing :

- Base material : internal HDD running normal CatalinaOS, external NVMe in a USB enclosure formated in APFS - GUID, external 64 Gb USB key formated to ExFAT - GUID (also tried with APFS).

-> I downloaded the sequoia installer with OCLP 2.4.1

-> I created the installer with OCLP on the USB key

-> I intalled OCLP on the USB key (at first I thought I needed to install it to the SSD so I also tried that and it didn't work either)

-> I reboot when prompted and hold the option key

-> Neither the USB installer nor the SSD show up as a boot option

I did the same thing on a 2013 macbook air and it worked fine (I mean, it runs super slow because it's not meant for Sequoia but the install worked)

submitted by /u/Magic-Baguette
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