Output video not matching input res or chosen aspect ratio

[Pathfinding]

I took a video with my Pixel 3 XL at 3840 x 2160 resolution and imported it to Shotcut.
When I created the job, I set the job resolution at 3840 x 2160. I also used this same resolution to set the aspect ratio. And I set the frame rate as the same as the video which was 30.01 fps.

But the exported video came out at 1080 x 1440 with a frame rate of 29.52 fps.
It also came out with black bars on the sides.

I know that all phones don’t have the same aspect ratio but as I’m uploading to Tiktok with an aspect ratio of 9:16, it would be nice to have it full screen rather than with the black bars.

I assume this is user error so can anyone tell me what I did wrong on not getting the same output resolution as input and also if there is a standard aspect ratio for Tiktok and other mobile social media video apps?

[PoisonedSlice]

@Pathfinding

When I created the job, I set the job resolution at 3840 x 2160

Do you mean the export job? Check settings → video mode and adjust accordingly.

Video Mode

Introduction Video Mode is the project resolution, aspect ratio, frame rate, and color space. It is important to set this as you desire at the beginning of your project. If you try to change it later Shotcut will try to retain the timing of edits, but some users have reported problems, and it is risky. Also, at this time Shotcut will not automatically adjust anything for you related to size and positioning of elements like text and picture-in-picture when changing resolution. You can think of…

Also compare the video mode settings to those found in the advanced tab after clicking the export button. Are they the same?