Help with 1.66:1 aspect ratio

I want to shoot a video in 1:66:1 format on bmpcc og, as I understand it, this aspect ratio is not in the settings and it cannot be created in any way?
When I create a project with an aspect ratio of 1:66:1, the top and bottom are displayed as letterboxes. The only option for them not to be is to scale the frame, or are there other options, since the quality becomes worse when scaling?
and tell me what resolution to use 1:66:1?

Short of some unlikely anamorphic arrangement, the only way to get 1.66 from a 1.77 sensor is to crop the image in post. If you want to avoid project lettering boxing you'd need to set timeline resolution to (I think) 1800x1080 (rather than 1920x1080), but your math may be better than mine.

That setting should still give you access to the sides of image which won't fit inside 1.66, using the pan controls. And of course you'd have to find an export format which allows that custom 1.66 aspect ratio, otherwise you'll end up with black bars on either side of a 1920x1080 frame.