base2 

You will find that rack or one very similar on about half of all bikes in the Netherlands. They are excellent for pizza, milk crates, yoga mats, bouquets of flowers, baguettes, and and whatever else you want to carry. The good ones mount to the frame independent of any steering action. Cortina is the brand I most associate with the one in the picture on the left. You'll find the 3 hole head tube mount on some Bromptons and occasionally on folding bikes, cargo bikes and other Minivelos.

I don't know your location, but here is one (Minivelo made or at least popular in Japan, I think) imported to the United States by Merry Sales/Soma https://www.somafab.com/archives/pro...argo-frame-set

As has been discussed, wheel flop is a consideration with load capacity. More rake/less trail will be less "floppy" & will tend to behave better than high flop, high trail bikes. Porteur bikes have very little if any to keep exceedingly heavy loads managable. High flop/high trail just requires more effort to effect the desired maneuver.

Frame mounted above the wheels contact patch/wheel axle is the best of the available options. As far as the bike is concerned you, the rider are just heavier that day. Low rider racks & hanging things of the forks invites all manner of complications into the mix because the load is an active part of any steering or balance function.