I've tried a few methods over the years to get a wild culture and had very little success over most beer starters left somewhere. Fruit can be done, but can still be a bit of a mold factory too and unpredictable. I was surprised, but tree bark is about the best and easiest way to get some wild yeast. Especially on my flowering and fruit trees. Yeast seemed to love those. I haven't really kept any of those though.
My best wild culture was a spontaneous ferment. I tried a few times before getting one to work, but simply I made a zero hop wort on my setup inside (during the spring when night time temps were still cold), didn't chill, pre-acidified, covered with cheesecloth, left the window open that evening and night, then racked into a fermenter. Took about a week to get going, but fermented out nicely. The beer didn't turn out all that great, but had some nice notes to it and became good blending stock. It was aggressively sour, and had a noticeable acetic acid component. It was also very, very thin. On the good side, it has a really delicate and great white wine, grape sort of flavor and a light funk that I knew could be harnessed. That was ~3 years ago when I captured it. Now after running more than a few beers from it, I've learned how to get some of the desirable flavors from it while holding back the acetic acid. I have even trained it to be able to run through a NEIPA sort of hop schedule and still provide some sourness (and it pairs beautifully with Nelson Sauvin). It isn't my best sour culture, but it provides some real nice depth in blends and I've used it to spruce up a couple of my sour cultures that are producing noticeably better beer with it.
I haven't ever made a mead, so no idea how that would translate and I'd expect the flavor contribution to be far different.