The backup failed with errors "error: could not connect to server: could not look up local user ID 1000: Too many open files" when the max_wal_senders was set to 2000.
The errors generated for the workers starting from backup worke=1017.
It wasn't the fact that you set max_wal_senders to 2000. It was the fact that you specified 1990 parallel workers. By so doing, you overloaded the machine, which is why everything failed. That's to be expected.
