2.3.5 brings a lot of stability fixes and continues the improvements to the product enabled by the new renderer and input/output systems introduced in 2.3.4. However, we also enabled the Inspector within the Sprite Editor, added new UI in Preferences to allow you to redefine the hotkeys GMS2 uses throughout the product, and introduced several other small quality-of-life tweaks which you can read about by following the links below.
There are of course also a number of important bug fixes, so (as ever) please do read the release notes carefully.