Yes. For star trails, the simplest workaround is to use an external shutter release with a built-in intervalometer. That lets you keep the camera in Manual mode with your chosen exposure settings and have the intervalometer trigger each shot at the interval you want.

Also check the Z6 reference manual settings for interval shooting. In Nikon’s interval options, some features behave differently depending on exposure mode:

• Exposure smoothing mainly applies outside M mode.
• In M mode, it only has an effect if Auto ISO is enabled.
• Interval priority is intended for P and A modes.

So if you want fully consistent star-trail frames, Manual mode with fixed exposure is still the right approach, and an external intervalometer is the most straightforward solution if the camera’s internal interval timer is limiting you.