I'm sorry to hear that the previous suggestions did not resolve your issue.
You're correct that if you remove the hard drive from your MacBook Pro and plug it into another computer, you would still need the encryption key to access the data. The hard drive is encrypted with FileVault, a disk encryption program available in Mac OS X 10.3 and later. It uses XTS-AES-128 encryption with a 256-bit key to help prevent unauthorized access to the information on your startup disk. Without this key, the data on the disk will remain inaccessible.
Additionally, physically removing the hard drive from a MacBook Pro, particularly models from 2016 onwards, is not recommended. These models use solid-state drives (SSD) that are soldered directly onto the logic board, making them non-removable.
At this point, your best option might be to bring your MacBook Pro to an Apple Store or an Apple Authorized Service Provider for further diagnosis. They have specialized tools and training that can help identify and potentially fix the problem.
Before you go, remember to tell them everything you've tried so far, and anything else you think might be relevant. This will help them understand the problem better and may expedite the troubleshooting process.
Hoping to hear good news from there.
Cheers bud!