The help section covers a lot of different problems. My problems are slightly old technology, I use an actual camera and not a smart phone. I have a lot of restrictions on my computer as well, but my primary problem is that my picture file size is too large.
I use this site here (no affiliations) because it is simple and doesn't set off my virus scanners:
https://www.reduceimages.com/
I use the defaults they provide and download there, uploading here.
I minimize my main internet window, which I've preset by now to a size that is about half the screen. My file manager screen comes up above that, I simply drag the picture from my camera to the box at the reduce image site. Again, remember to download not just resize.
When you get to the attach screen and have the option to browse you should have one at the top already defaulted to your download directory and there you go! Once here it took my far longer than you would think to realize the attach screen is incorrectly shaped. You have to widen it out to a horizontal format (it comes up in a vertical) to get the Upload button.
Edit: I have vision issues and have made things to default in my file manager so if they are pictures they show me a small image, not just the file name. That saves a lot of clicking!