Question about Lian-Li PC-O11DX Dynamic

Yes, with a vertical GPU you definitely get enough air circulation from the bottom to the top. What you have to bear in mind, however, is that there is pretty much exactly 3 cm between 120mm fans on the bottom and an ATX mainboard, and the 120mm fans (25mm high) also cover about 5 mm of the bottom edge of the mainboard. So if a connection needs more than 3cm (in my case the USB 3.2 Gen 20pin), no fan can be mounted in front of it at the bottom.
There are many factors that contribute to the heat in the enclosure, so a generally valid answer as to whether 3+3 is enough is not possible. I bought the case first and with my old PC (i7-860, GTX 970) I had no heat problems even with only one fan on the bottom (in), one on the side (in) and one on top (out). Currently I still have the 970 horizontal and a Ryzen 5 3600 with 2 fans on the bottom (as the 3rd currently has no room), 3 in from the side (in) and 2 on top (out) and no heat issues.