MSI B550-A PRO Motherboard Doesn't Boot Ubuntu

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About a week ago, I upgraded most parts of my PC except for the case and GPU. I then wanted to remove the M.2 SSD from my Acer laptop into my PC and thought it would be plug and play but my PC won't boot from it. Instead it just asks me to insert a bootable drive. Can anyone help?

• More information

  • Motherboard: MSI B550-A PRO

  • OS: Ubuntu 20.04.6 LTS

  • M.2 SSD is LUKS encrypted

  • I had to flash by motherboard to the latest drive (version 7C56vAH) because my CPU (AMD RYZEN 5 5600X) wasn't supported with the old driver and PC couldn't post

  • I have windows 10 installed on a SATA HDD, but PC doesn't boot or detect Ubuntu even if I disconnect it

Anyone know why this is happening? I suspect it's a motherboard setting because my laptop boots Ubuntu. I've tried switching between CSM and UEFI alongside enabling and disabling secure boot but Ubuntu just doesn't come up nor does it show as one of the boot options when I switch to CSM.