Here's the latest ESO datamine (January 2022) from the Update 7.3.0 and the Ascending Tide DLC on PTS. It adds promotional banners for new Crown Store items and the next Crown Crate Season (Sunken Trove Crates).
Reefborn Mounts seem to be the Apex rewards in the Sunken Trove Crates while the Radiant Apex Mounts are probably the Cat o' War Senche Lion, Coral Crawler Dwarven Spider and Surfglow Courser.
Other items that might be in the Crates are the usual Adornments, Body and Head Markings, Furnishings, two Outfit Styles (Keptu Chief Armor and Reefborn Arms Pack) and three Skins (Culanda-Born, Labyrinthian Luminary and Rainsiren Nereid).
There are also new Costumes, Hats and Emotes as well as regular Mounts and Non-Combat Pets, including the rather funny looking "Catwell".
Two new Undaunted Arms Packs this time are Lady Thorn and Prior Thierric, and we also get another Arms Pack called "Saberkeel Armaments".
This update also adds one new House (Seaveil Spire) and two Houseguests, one of which is Jakarn.
Finally, there is Giladil the Ragpicker, a new Deconstruction Assistant.
Be sure to also check the previous datamine from the Deadlands DLC if you haven't seen it as some items from it haven't been released yet.
If you want to discuss this datamine with other ESO players, you can join the ESO Model Viewer Discord server.
Keep in mind that these pictures were found in the game files and the items pictured are not officially confirmed. As such, they might change significantly on release or might never be released at all.