I’d argue fixing a flat on a IGH or fixed gear/single speed is easier than a geared bike. Hardest thing about a single speed is needing the proper tool to remove the axle nuts, but after that take the chain off the cog and the wheel will slip right out, just as easy to put back in, just reverse the process. Getting chain tension can be tricky, but tighten the drive side bolt first at the point the chainline has about a centimeter of mesial play and once you tighten the other bolt the chain line should be spot on.

Where a geared bike with a derailleur will need you to put the bike in the smallest gear, and untangle the chain from the cassette. Replacing the wheel back in requires the chain to be properly laced around the cassette and can require dexterity.

Unfortunately derailleurs are necessary to ensure chain tension when the bicycle frame isn’t designed the allow for manual chain tensioning (vertical dropouts).

Also, run tubeless and flats will feel like a thing of the past.