I've been using clipless on my gravel bike, but when i built up my Surly ECR with RF Chester flat pedals (for slower, more casual riding, especially when loaded for bikepacking), i rode in some worn Oboz hiking shoes. It was nice, doable, i don't think i was missing much compared to the advantages. I lost grip a lot, but the soles were worn. I just picked up a pair of these and they may work out great for flats. I haven't had a chance to ride yet. Not as big and clunky as my Five Ten Freerider Pro MTB shoes
https://www.jensonusa.com/Five-Ten-T...woSolar-Red-75
eric/fresno, ca.