Attaches to the back of the X1C using magnets. Uses 6x3 magnets and should be printable without supports. The filter I used is at https://www.amazon.com/dp/B083TJY3MY and it's a HEPA vacuum filter. The filter comes with a tab attached, and you'll want to cut it off with some flush cutters or some scissors. There are spots for six magnets on the grill/cover but two magnets on the cover seems to be plenty for me.

This is a remix of a remix.

The original is by cushmail here (uses 5x5 magnets): https://www.printables.com/model/368465-bambulabs-x1c-magnetic-hepa-filter
The remix that I remixed from is by timmerken here (uses 6x3 magnets but requires supports): https://makerworld.com/en/models/97864
I ended up remodeling timmerken's version so that it wouldn't require supports. If you like this design, please thank them as well for their great work.