Probably the most important thing you can do for your microbiome is eat enough fibre. Eats some beans and some carrots. Cut back on the high fructose corn syrup and save antibiotics as a last resort.
Do not rely on various forum threads, you could read bad diagnosed people or diseases you should not care about.
Probiotics are like a mercenary army that you can bring in when some pathogens are causing havoc or the equilibrium is very disturbed. They generally don't stick around permanently but they help outcompete the nasty microbes. Unfortunately, they also compete with the good microbes in many cases (the "standing army").
We really don't have a good process to restore the species that get lost through antibiotics and bad diet other than good diet for a long period of time (a wide and balanced variety of whole plant fiber) hoping the good bacteria will establish themselves again, or a fecal transplant which has all the risks of a blood transfusion if the donor isn't screened thoroughly.
The current science is still unclear about which bacteria combo is important, in which proportions, in which part of the GI system. BUT we do know gut flora is important.
So my approach is to consume (in moderation but regularly) a variety of fermented foods that come from traditional cuisines. Yogurt with a wide variety of active cultures, Miso, Cheese from unpasteurised milk, Kimchi, etc.
Also raw vegetables will likely have traces of microbes from the soil they were grown in, though I have no idea what role those play, if any.
[1] https://sciencetrends.com/restoring-gut-health-the-benefits-...
https://www.visbiome.com/blogs/news/maryland-federal-jury-un...
My personal supermarket favourites are sauerkraut, tempeh, kimchi, miso (I put miso paste in everything...), kombucha, and pickles. Basically any fermented food really.
I recommend trying to make some of your own if you find the time. I make dosa quite often on the weekends, which is a kind of delicious Indian pancake. Also tried my hand at making Natto, which is this strange but delicious sticky soybean thing. Had Salgam in turkey which was amazing too (it's a weird salty, spicy, fermented pickle juice).
Check out Wikipedia for a reasonably complete list: https://en.wikipedia.org/wiki/List_of_fermented_foods