I ended up solving the issue by finding an old machine running MacOS version 11.6.4 at work which had an older version of LibreSSL. That machine let me run the decrypt command like I did previously on my machine - problem solved and I will NOTnot be using GCMaes-256-gcm
for this in the future.
Thank you to everyone for your ideas. I knew walking down the path of downgrading was going to be a nightmare most likely and could break something else.
This is by far an area I'm a novice in so thank you Cpt.WhaleCpt.Whale and Gordon DavissonGordon Davisson for offering helpful guidance.