Can I slightly rotate a shape in Preview or photos Markup?

If you are using a trackpad with your iMac, visit System Preferences > Trackpad panel and select Rotate in the Scroll & Zoom tab. Now, once in Preview, you can rotate your image by the amount you prefer, by using your thumb and index finger in a rotating manner on the Trackpad. No need to click on the trackpad. Unfortunately, there is no reporting of the degrees rotated as you are doing so.

Without a Trackpad, Preview only offers 90-degree rotational increments.

In Photos, make image full size then check Edit in top menu right. Check crop in center menu, click on picture then adjust rotation with wheel pointer on right side of picture then click done and the picture will be saved back to Photos.

I don't believe Preview has that capability - it's a basic app; do not know about markup since I've not used it. You will most likely have to look for an app that will allow you to edit and manipulate images. Probably not a free app. Affinity photo is one I know has that option:

https://affinity.help/designer/en-US.lproj/index.html?page=pages/ObjectControl/transform.html?title=Transforming%20objects

You can rotate shapes you create in Pages:



MtD