It's pretty easy to do, I used Irfanview picture viewer > Image > Colour correction to desaturate the image, then crank up the contrast to get a rough vector-ish image, then Image > Effects > Pixelate.
If you have a large image, and you want it to have larger "pixels", then you can use Image resizer for windows to resize to a custom resolution (say, 200 x 200 px) before editing it in Irfanview.
In the past when I have had to do this on windows I used a Power Toy which somehow still exists and is getting incorporated into Win10 Power Toys:
https://www.bricelam.net/ImageResizer/
Now I know this is not natively in PS but it was always reliable, quick and easy and you could do batches of pictures.
Not sure of Macs but hope this helps in some way.
I'm assuming you run Windows, which I haven't for years, so I don't have any first-hand experience with any recent applications, but the freebie Bricelam's ImageResizer gets a few mentions. Here's a guide on how to use it. You can install it by itself or as part of a pack of utilities called PowerToys.
This little tool changed my life (I have no affiliation) https://www.bricelam.net/ImageResizer/ You can resize multiple images at once using your mouse and right click. The results are consistent and great quality.
Generally I try to export from the software I am using at the resolution I want, but when I have a bunch of pictures (on windows) I use this which is basically the window xp power toy "image resizer" rewritten by someone to work on windows 10. Its works by simply selecting all the photos, right clicking, and then clicking resize.
I use Image Resizer for Windows to quickly resize a group of pictures. This will just resize the photos to get into whatever dimensions you need but you'll still need to crop or do any other editing you need.