Macbook pro 16inches 2019 fails to reinstall catalina on recovery mode after erasing hard drive, and T2 chip dissallows to boot from external drive
This is how I solved the issue.
You need another Apple computer running Catalina.

Make a time machine backup of the working computer.
Boot the non-working computer in recovery mode.
Recover from that backup.
Continue from there...

Hope this helps other people.