Windows 11 Themes |best| -

Official themes are safe but limited. They cannot change the shape of the Start Menu or the transparency of the taskbar. To go deeper (making Windows look like macOS, Linux, or retro Windows versions), you need third-party tools.

Disable via Settings > Accessibility > Visual Effects if UI lags. Set image rotation intervals to 1 hour instead of 1 minute. Troubleshooting Common Theme Issues Taskbar Disappears or Freezes windows 11 themes

The quickest way to change your look is through the Settings app. Official themes are safe but limited