Flash rovery with fastboot and adb.
Flash the original fastboot recovery software for your device.
This will normally work if everything else does not.
I am afraid your partition is encrypted. There is no way to decrypt it without formatting your internal storage.
Use orangefox as recovery instead of TWRP. Orangefox is more stable.
I use magisk 20.4.
Did you try formatting data partition. Install latest Rom. Do not restart but flash Magisk 20.4 immediately after Rom. Then reboot to system.
In magisk I use the systemless mode