I'm aware the deadline to file taxes is April 15th, would it be best to risk re-mailing them? Even so, I just want to e-file in case. Would this also affect any amended returns?
Did you file an Amended return for 2023? You shouldn't file an amended return until the first return is fully processed and you got the first refund or paid the tax due. How do you know they were lost in the mail? Did you get a tracking number from the post office when you mailed it?
You can switch to efile but if the IRS gets a mailed return and an efiled return it will delay your refund.
In TurboTax Online, sign in to your account.
Select Tax Home in the left menu.
Scroll down to Your tax returns & documents.
Select 2023, and then select Add a State (you're not actually adding a state, this just gets you back into your return).
https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online/00/26985
If you have a refund there is no penalty if you file after April 15, 2024. You have 3 years to file for a refund.