Document and export large format documents as 300dpi

Being able to set new document as 300dpi and export at 300di would be a great help for me, I produce poster size graphics, max export size pix of 8192px is too small for anything larger than A2 or #x24”, I need up to 12,000px or larger, I have to export as jpg and paste into a Affinity Graphic document of the correct size and dpi to achieve 300dpi.

Max size from Vectornator is 27” @ 300dpi which is very limiting.

My printer demands files at final print size and 300dpi.