I am concerned that I won't be able to read incoming encrypted emails without the key working.

You need the private key to read incoming messages encrypted to your public key.

I successfully imported the public keys from Linux to Windows for several email addresses, using a single export file for all of them. For some reason, there are four that won't import. This time I exported all four in one shot, but when I tried to import them, I got this error: Error! Failed to import keys. RNP.importToFFI failed. The keys are still listed in the OpenPGP Key manager.

If I were to copy the profile directory from Linux to Windows, would that solve it?

At one point I successfully imported several keys via Key Manager. Those email addresses have keys now. But there are several that still do not.

So, I tried again. It appeared that I successfully imported five keys for five email addresses that have keys in the Linux machine but have no keys in the Windows machine via Key Manager, but the email accounts still say there is no key. I opened Key Manager and selected a key for an email address that says it has no key, and right-clicked, and selected Key properties. I chose: Yes, I've verified in person this Key has the correct fingerprint. I then clicked OK. But still, nothing happened. The email address has no key. OK, what am I missing?

I published the pubic keys, thinking that might help. Now I read that that's a bad idea. Great. Should I revoke them?

On the Linux machine, I just revoked all of the keys I created two days ago. I then hit "Publish" again, as that is what the instructions said, to update the keyserver that the revocation had taken place. There was only one of the new ones that transferred over to the Windows machine, and I had to revoke it again on that machine.

I will l have to create new ones.

There are still email addresses with older keys that I did not revoke, that will not transfer from the Linux Thunderbird to the Windows Thunderbird.

If anyone can help with getting these keys to transfer, I'd really appreciate it.

This time I exported all four in one shot, but when I tried to import them, I got this error: Error! Failed to import keys. RNP.importToFFI failed.

Is there anything special with those keys? Try to export each key individually instead of multiple ones in a single shot. As said before, if these are personal keys, you'll have to export them with the private key. I.e. you'll be prompted to set a passphrase for the exported private key. Please confirm whether this is what you're doing. Is there anything in the error console (Ctrl-Shift-J) after attempting to import a key? When importing a key, please explain the exact steps you're doing.

I succeeded. I exported the Secret Keys from the Linux system and created a password, then imported them successfully into the Windows system. Then, transferring the public keys worked. Thank you for your help!