It can be easy to overthink it, but I agree with the posters who's sentiment is "just get on a bike and go" - this is how I started.

As a teenager in the country the next town over was an hour bike ride in any direction so I would just hop on my department store mountain bike and start riding, absolutely no tools or gear with me.
Thank goodness I never got a flat while doing this for several years. That would have been a "fun" lesson to learn in the pre-cell-phone era. lol

The gear does get accumulated from experience though.

I did eventually get a flat during a long ride around the city a few years later and would have had to walk back home in the rain had a kind stranger not taken pity on me and patched my tire.
So when I started commuting by bicycle I used an old 10 speed to ride 20km to work and back many days with some tools and a pump so as to not get stranded again due to a flat.

After a few rides, I put a rack on to get the back pack off of me so I wouldn't be as sweaty from the ride.
Rainy days and muddy trails led to getting fenders.
Then I added lights as the season changed and I was more often starting off and ending my ride in dimmer light.

This all led to my basic commuter setup which I also configured a bike for my wife to use - any-bike-you're-comfortable-on + rack/fenders/lights/pump/patch-kit.
Other people have different experiences and likely have other pieces of gear they feel they need, or different ways to solve the particular challenges they've faced while riding.

I think once you've been at it for a while, the items you've accumulated to make your setup work for you become "essential" in your mind because you remember when you didn't have those items and why you ended up getting them.
So when someone comes here and asks "what do I need to get started?" there is a tendency to give them a shopping list and say "this is what you need".