Hot take: My sourdough starter from 2019 is a completely different beast now.
It went from a sluggish, barely bubbly mess that made dense bricks to a vigorous, almost foamy monster that reliably gives me an open crumb after I finally started feeding it with a mix of rye and whole wheat flour instead of just white.
Honestly, have you ever thought about the wild yeast in your kitchen air changing it too? Tbh that starter is basically a living record of your home's whole microbiome now. Ngl it's less about the flour and more about it finally adapting to your specific house.
But a starter is mostly just eating the flour you give it. The air in a kitchen is pretty much the same everywhere, and commercial yeast is in most homes already. Changing flour type or feeding schedule has a much bigger, faster effect. It's more about the food source than catching some special bug from your ceiling fan.
My 2019 starter spun off into its own yeast empire around month 4, I swear it started staring at me through the jar. @hannah_wells you basically described my kitchen as a biohazard zone, thanks for that image while I'm eating toast. I feed mine straight tap water and whatever flour is cheapest, so my "house microbiome" is probably just mild regret and a faint smell of gas station pastries.