Is Smart Slider Joomla 4 compatible?
Yes, Smart Slider is Joomla 4 compatible!
So if you want to do a new installation, follow these instructions.
If you want to update your Joomla 3 website to Joomla 4, you might see Smart Slider as "Potential Upgrade Issue". That happens, because of Joomla's cache. You can ignore that message or follow these instructions.