I used Photoshop to reduce the size of the photo that I used for my avatar. Go to Image>Image Size. Actually, you might want to duplicate the image first so that you work on a copy (Image>Duplicate). That's what I did.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365