I've tried to word this as accurately as possible because it's a weird problem. I've searched Adobe as well as Google, and no luck. I'm using Photoshop CC 2022 (23.3.1) on both iMac (2020) and Macbook Pro (2019). Both Macs running OS Monterey 12.3.1. Plenty of RAM and scratch disk space on both. Photoshop preferences are identical on both. On the iMac, the Eraser (hard round brush, hardness, flow, opacity all 100%, cursor is "normal brush tip") erases all the way out to the edge of the cursor circle, just as I've always been used to. Yet on the Macbook, it only erases to about 3/4 of the diameter of the cursor circle (see screen shot), which makes it really difficult to do any kind of accurate work. PLEASE NOTE - I am not a power user. I've used Photoshop for simple tasks and have been satisfied. This new wrinkle is totally out of the blue and seems to be hardware-related, which I've never heard of. Any insights?
Quick update to my post: Don't know why I didn't try this before, but the same problem happens with the Brush tool as well. I position the round cursor, click, and the fill only comes to about 3/4 of the circle diameter. Is there some underlying setting I'm missing? As I said, preferences on both Macs are identical, but I'm unfamiliar with brush settings, etc. Thanks.
Yes I did, and no joy. But - thanks to the luck of the draw and some suggested other threads - I did find the solution. And it's as weird as the problem. Basically, the size of the cursor and the actual size of the brush/eraser in Photoshop are affected by a setting in System Preferences -> Accessibility. Here's the discussion that did the trick: