Goal:

• tap capslock: maps to ESC
• hold capslock: map to CTRL

File: /etc/interception/udevmon.d/caps2esc.yaml:

# caps2esc -m 1 := map caps to esc/ctrl
- JOB: intercept -g $DEVNODE | caps2esc -m 1 | uinput -d $DEVNODE
  DEVICE:
    EVENTS:
      EV_KEY: [KEY_CAPSLOCK, KEY_ESC]

The -m 0|1|2 meaning:

    -m mode    0: default
                  - caps as esc/ctrl
                  - esc as caps
               1: minimal
                  - caps as esc/ctrl
               2: useful on 60% layouts
                  - caps as esc/ctrl
                  - esc as grave accent
                  - grave accent as caps

Make sure that the udevmon.service is running.