Can individual setup payment gateway like stripe easily?

Legally, yes. Stripe isn't that deep. It processes credit cards in every country. It makes sure that wherever you are, you can pay someone else in any other city.

Most countries will want other payment options too - banks, some ewallets, 7-11, QR, phone credit. Some of these have unexpected rules, like downtime at 1-3 AM, or a hefty fee for certain transactions between bank. And then you have workarounds where the PG has accounts in all the banks, and processes transactions from bank H to bank I by making a H to H' transfer and an I' to I transfer. Where ' is the account owned by the PG. So local players often beat global players in these as they can go cheaper, faster, more reliable.

And so many global payment providers will build on top of local ones for many different countries.

You can use Stripe as an individual. There is basically no vetting from my experience. For example, if you get donations on Buy Me A Coffee, they pay you through Stripe.

If you're specifically needing something like stripe in order to charge customers in dollars (or any well known currency), and are limited by your local options, consider a Merchant of Record like LemonSqueezy, Paddle, or Gumroad.

They're usually fairly open to sole proprietor (no registered company) businesses in many countries.

Probably depends mostly on the payout country (where you are located) that will drive KYC requirements from the processor (stripe, etc), where people are paying you from (currency acceptance), and a little bit on what you are selling (e.g. subscriptions need a little more infrastructure).

“Non-US” could be any of 190+ other countries. Where specifically?

Isn’t there something like “private propriotorship” thing?

Stripe supports individuals ar least in 1 non us country i know of.