You can sequence PC messages, they are moving the sequences forward in the Digitakt, you just need to send the change slightly before you want the pattern to change.
That means - if you have 64 steps (4 bars) programmed on the Digitakt - you should send the PC message at step 63 of the current pattern, so it triggers the switch to the next 4 bars.
You control the length of the pattern with master length - for ease of use, set it to the same length as you step length of the pattern. If you have shorter patterns, you can change that setting.
You send the program change on the “auto channel” you set this up in global.
(the thread about the pyramid, but its the same behaviour)