MacBook Pro keep asking me login in after I login in

I believe this a macOS bug which I've encountered before where only (n - 1) users are listed on the login screen. The first login screen you see is unlocking the Filevaulted drive and the second login prompt is asking to actually log into your account which isn't available due to the macOS bug. To "fix" the issue we need to create another user account so your original account shows up again.

If you are using a pre-2018 laptop you need to boot into Single User Mode by pressing & holding the Command + S keys just after powering on your laptop. After unlocking the Filevault you will see a black screen with white text scroll by, but then you should see a command prompt, if you don't see the command prompt, then just press the "Return" key which should present you with a command prompt. At the command prompt type each of the commands and press the "Return" key at the end of each line to submit the command. These commands will force macOS to run Setup Assistant again when the laptop reboots so you can create another admin user account.

fsck  -fy
mount  -uw  /
rm  -i  /var/db/.AppleSetupDone
reboot

If you cannot boot into Single User Mode because you have a newer 2018+ laptop with the T2 security chip, then let me know and I will provide another set of instructions for you.

Enter your password for your user account as this will unlock the Filevault so you can boot the laptop. Once you do the display will go to a black screen with white text scrolling by which indicates Single User Mode. Run the commands I listed while in Single User Mode.

After entering the commands in Single User Mode, the laptop will reboot and prompt you to unlock the Filevault again using your regular username and password. Once you do this Setup Assistant should walk you through setting up the computer again with a new admin user.

It is an odd situation. Filevault knows about your user account, but macOS itself no longer recognizes your user account as valid. Technically you can have a different password for your user account and Filevault, but macOS normally just combines the two together so this ability for two passwords is hidden from the user.