I had the idea of a seal, like the instance icon, in an ancient greek style, like on pottery, but I couldn't find any public domain or similar images we could use for free and I'm not an artist myself
You might have done this judging by the red coloring of some of them, but did you try something like "athenian red-figure pottery" since apparently that's what it's called?
How about we get rid of the pottery try to keep it simple
A tondo in the Athenian red-figure style depicting a seal
A tondo in the Athenian red-figure style depicting the satisfied seal meme
An Athenian red-figure depiction of a seal
An Athenian red-figure depiction of the satisfied seal meme
If it comes back with like governmental or organizational type seals, then maybe we switch "seal" to "pinniped". Or "Mediterranean monk seal", which is apparently (one of?) the type(s) of seal around Greece.
Or that doesn't work, I don't know. I'm not versed in AI image creation so I don't know what limits you have or what works and doesn't work.