There is a one second delay after finding the new port (after the touch_1200 reset). The comment says it is needed for OS X. On Linux, I find that 95% of the time the boot loader has already timed out by the time the programming is ready to start. This could be an issue with the boot loader, of course, but rebuilding arduino-cli with that delay removed resolves my problem.

Current Behavior

$ arduino-cli upload -p /dev/ttyACM0 -b arduino:avr:micro
Connecting to programmer:

Then it hangs.

Expected behavior

With the delay removed:

$ arduino-cli upload -p /dev/ttyACM0 -b arduino:avr:micro
Connecting to programmer: .
Found programmer: Id = "CATERIN"; type = S
    Software Version = 1.0; No Hardware Version given.
Programmer supports auto addr increment.
Programmer supports buffered memory access with buffersize=128 bytes.

Programmer supports the following devices:
    Device code: 0x44

and the sketch is uploaded and started correctly.

Environment

• CLI version: arduino-cli Version: 0.21.1 Commit: 9fcbb39 Date: 2022-02-24T15:41:45Z

• OS and platform: Ubuntu 18.04