The bottom right spinner here:
animates in Chrome and Safari as static HTML. But when added into an LWC - meaning the content is dynamically added to the DOM - it animates in Chrome but does not animate in Safari.
I presume the problem is unrelated to this fixed problem CSS animation in LWC not working, and has more to do with Safari. Things I found Googling such as adding a start delay didn't help:
animation: cssload-dots 3.25s infinite 0.01s ease-in-out;
I think this is worth flagging that here for anyone thinking of adding animations to their LWC. And if there is a reliable answer to how to fix this, that would be great too...
Don't see any mention of Safari in the change history of the SLDS spinner.