If it wasn't clear enough from Samsung's statement that the Galaxy S21 Ultra will gain support for the S Pen, it's clear now. An FCC filing for a Samsung SMG998B (Galaxy S21 Ultra) in testing has listed support for a "stylus device" with both "hover and click and an operating range of 0.53-0.6MHz".
So we can now take it as confirmed that the Galaxy S21 Ultra will have S Pen support when it launches on January 14. Whether Samsung has made a new S Pen or will use the one from the Galaxy Note20 Ultra is unclear.
The FCC report also points to wireless power share on the Galaxy S21 Ultra, which means that it can charge wireless earbuds (like the Galaxy Buds Pro, which will come alongside the Galaxy S21 family).