Render job fails when choosing quality manually for 4K files

Hello fellow Davinci users,

I have faced an error for a while and did not find any solution despite having thoroughly searched online.
I usually work in 2.39 resolution with timelines of 2048 X 858. When I go to quality and choose "restrict to" in spite of automatic, I can input manually the KB/S. I usually choose 20000 KB/S for 2048x858 and the render job is done perfectly. However, if I choose a resolution of 4096 X 1716, if I decide the KB/S manually it gives me a Job render Fail. But if I choose automatic, the render is done.
I have tried various KB/S rates (50000, 30000, 60000, etc...) and it always fails in 4096 X 1716 resolution. But in 2048 X 858 resolution it works. It happens on all my project. I have tried on 7 projects and the render fails with manual quality KB/S in 4096 X 1716.

Does someone knows how to sort out this issue or why does the render job fails.

I have Davinci Studio 18.1.2 and working on an iMac 5K, 27", Year 2017, 4.2 Ghz with an updated SSD drive and working with Sandisks SSD portable drives as well.

Thanks for the help.

Which GPU?
I'd render out in ProRes 422 HQ, which never failed me, and compress with HandBrake.
I had that machine as well, with the 580 and an eGPU, 580 too.

The GPU is a Radeon pro 580 with 8Gb memory. Indeed the work around in ProRes is a solution. But I would like to understand why it does not work under Davinci.

Thanks

If it works in lower resolutions and fails when going higher, it’s a limitation of the hardware.
A GPU with 8 GB is plenty for HD or 2K, but barely enough for 4K.