Look in your account for the certificate of electronic filing -- it will be with the pdf of your return. Or look in your online account to see if it says the 2018 return was accepted. Or does it say "rejected", "printed" or "ready to mail?" If it does not say accepted, it was not filed unless you mailed it in an envelope and took it to a mailbox yourself. Not sure why you have waited this long---did you recently receive a letter from the IRS? What has you looking for a 2018 return now in 2025?
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**