Photos using just about any camera or phone are so large these days it is sometimes difficult to upload to sites with size limits, or when your Internet connection is slow enough to make it painful.
I like to size all my images to no larger than 2048x2048 because that is what Google Photos allows in order to keep unlimited numbers of photos for free. I use an image viewer called Irfanview which you can use to batch resize as many photos as you like. For example, if you have a folder full of pictures, you can have Irfanview resize them all automatically to whatever dimension you like.
The program is (and always has been) free, with no advertisements, and runs on Windows. It is definitely the fastest and most useful image viewer/manipulator I have ever used, and I've been using it for over 20 years.