I have no idea what people are complaining about.

In Photos you can create as many albums as you like. If you don't organize your photos into albums then, yeah scrolling through the library of all the photos will be a PITA. But even then, they'll be organized by year and month.

I can select the photos I want and then I have several options about how to move them somewhere else.

Airdrop to a Mac or other Apple device.

Mail them or send them in a text message.

Move them via WhatsApp.

Or download them to Google Drive.

Someone else mentioned iCloud already. Your photos are automatically uploaded there and you can easily access them through a PC web browser.

I also have iXpand meaning I have a SanDisk thumb drive I can put into my phones lightening port.

Why people are talking about iTunes is a mystery to me. iTunes went away years ago.

You may even have an app for your camera. I have a Nikon app that allows me to upload Gigs worth of photos. I don't use it because there are so many other options.

Other than the iXpand, all this is done via WiFi or Cellular.

You don't say what social media you have to upload the photos to, but I've done it to Craigslist, Zillow, Reddit and others I don't recall, through the Safari browser.

You say you want to share photos from your PC to the phone and then to Instagram, I'm baffled by that sequence. How did you get the photos to the PC to begin with? Why can't you go straight to Instagram from there?