is it safe to use 50% there?

hey, im working on tiny recreation of a figma design and i came across this. i know that the best thing i could do is using subgrid, but sadly to this date, subgrid isn't fully supported yet. im thinking of splitting this using flex basis 50%, basically header has colspan of 2 and inside the header, there would be 2 navs, one on the right and one on the left, is it ok to do it like so? the layout itself is easy but im not entirely sure if this is the right thing to do.. and yes, that image has rowspan of 2. thanks for any help <3 design taken from: https://dribbble.com/shots/23283777-ai-picture-generator-0