It was just mentioned I'm not eligible for e-filing. Why is that?

No one in the user forum can see your screen or your tax return.   We do not know why you cannot e-file.   Are you trying to e-file a current year 2024 return?   Or are you trying to e-file a past year return?   Only a 2024 return can be e-filed; past year returns must be filed by mail.

I'm filing 2024 tax returns. I'm a US citizen, born in USA, but have been living in The Netherlands since 1993, working for employers based in The Netherlands. Is that a reason I'm not eligible?

Many, many ex-pats are able to e-file their tax returns, so something else must be standing in your way.   What is the EXACT message you are getting when you try to e-file?