Are you sure about this below that you upgraded the 4 yrs old wallet to 3.3.8?
Anyhow, I just started me software up, 3.1.2, and now four years later I upgraded to 3.3.8, and when trying to send funds, I get a password invalid error.
Electrum 3.1.2 was release 2 years ago around 2018 so what I'm thinking is either you installed a fake Electrum 3.1.2 4yrs ago or the version you are talking about is 2.7.x which was released around 2016?
If it was 2.7.x version you will experience some compatibility issue if you upgraded it to the latest version
But if not and it was 3.1.2 and if you make a mistake on the year you mentioned it should be work after you upgrade it to 3.3.8 because I have a wallet file which was generated on 3.1.2 wallet and use the latest version without any issue.
Can you try to install the 3.3.4 version and import the wallet file(Follow the nc50lc suggestion) then test it again.
If you still have the error about the password well, I think you will need the help of BTCrecovery about the password.