Performance, clipboard behaviour, and file browser persistence seem like fairly typical OS-specific issues. Obviously not great if they're not properly testing macOS, but I don't think it's an "even bigger red flag" for those to be OS-specific.
Grouping close-together changes of the same control for undo sounds probably intentional to me, like how Ctrl+Z in a textbox doesn't go one character at a time, and if I move something with arrow keys I'd expect that to be one "movement" once I stop rather than one per key repeat. Whether it's grouping too aggressively to the point of being recognized as an issue is probably down to personal preference, though I would lean towards agreeing that less grouping would be better.
Grouping close-together changes of the same control for undo sounds probably intentional to me, like how Ctrl+Z in a textbox doesn't go one character at a time, and if I move something with arrow keys I'd expect that to be one "movement" once I stop rather than one per key repeat. Whether it's grouping too aggressively to the point of being recognized as an issue is probably down to personal preference, though I would lean towards agreeing that less grouping would be better.