There is no difference between the two in meaning

In theory you could use both but I think Adding in “to be” rather superfluous or unnecessary.

They're both the same. The second one just "feels" more grammatically complete. For me, I might add a "quite" to both for it to be more comfortable. I found him quite interesting. I found him to be quite interesting. But that's just me. Happy learning!!

you found who interesting?