Unbootable OnePlus 5T
Since you've installed TWRP, you cannot lock the bootloader. A locked bootloader will perform integrity check at boot time and if it finds anything tempered, it will refuse to boot:

The solution is simple: Unlock it again. You won't lose your data this time, so just proceed to connect your phone to a computer, boot into bootloader mode and run on the computer:

fastboot oem unlock


Exactly like when you did before rooting. This will make your phone boot up again.

Additionally, you may want to check for a newer version of TWRP and see if some bugs are fixed so you can do the data wipe.

For the problem of Freedom messing up Play Store, you can check out this answer.