Is there a way WITHOUT iCloud to move your text messages from your old iPhone 6 to your new iPhone 8 (I don't remember the encryption code)?

Is there a way WITHOUT iCloud to move your text messages from your old iPhone 6 to your new iPhone 8 (I don't remember the encryption code)? - 1

No.

Even if you back up the old phone to iTunes on a host computer, then you're going to still need to enter the security credentials for that phone to restore the backup to the new phone.

Apple provide ample means for genuine owners to recover their data if they forget their phone PIN code, and also for recovery of iCloud credentials such as your Apple username and password. If you've lost all access to those details then you've been careless and the price you pay is loss of your data. Just as with any other similar security system.