Welcome to Endless!
Our Raspberry 4 image is released as a preview. It does have known issues mentioned in this thread and a few more in the release notes.
All of the core OS functionality should be equal to our regular PC offering. App support is rather good, but there are a handful of omissions, such as the Terminal Two coding games not being available (because Unity does not run on ARM64 Linux). Also Skype, Chrome, Steam are not available as those proprietary software packages are not provided for ARM64 Linux by their vendors.
The biggest item to note is the lack of hardware acceleration, so you will observe that the interface feels sluggish compared to other OSes that you can run on RPi. But this does seem subjective and perhaps dependant on what you want to do with the device - while some think it is unusably slow, others think it is good enough as a starting point! Here is a recently produced community video that will give you some insight into the performance:
We will also be adding graphics acceleration as soon as support is fully implemented by the upstream Linux community, and there are some big steps being taken in that direction at the moment.