For a while when I started brewing I used iodophor diluted as I had found recommended online as a sanitizer, worked pretty well to prevent infection. I just used the medical grade stuff (either iodine-povidone or tincture of iodine) diluted to about 12.5 ppm. At this level it should be no rinse.
I’d say try google for more information but it’s full of crap bot-generated articles now, so that’s gone. I mean, I found an article suggesting you use vinegar, baking soda and salt to make a sanitizer. Don’t, by the way.
I switched to starsan because it was more convenient and doesn’t smell like a hospital when using it. Starsan is basically phosphoric acid (same thing they add in coca-cola for example) with some surfactant mixed in.
If you don’t use any sanitizer your main issue will be beer tasting off due to contamination from wild yeasts, or bacteria. This becomes more of an issue when bottling, because wild critters can usually ferment more things in your beer than single-strain lab grown yeasts (except diastaticus, that thing is a beast), and over time they can eat through residual sugars in your beer and generate more alcohol and CO2 - so potential bottle bombs, worst case.
However, if you do want to go the rustic route, there are some books out there describing historical farmhouse brewing techniques, some still used today (and they didn’t have starsan).