It's not that direction.
If you put a piece of wood 65mm on the saw it will not cut all the way through it; the blade only sticks out of the bottom of the saw by 64mm. If you put a 65mm thick piece of wood on the saw and cut then you will have a single piece of wood at the end, that looks like two blocks of wood joined by a thin 1mm strip at the bottom of a narrow gap between the woods
"At 90 degree bevel" means "when the saw is tilted such that the blade is vertical relative to the bed on which the wood you're cutting sits. For saws that tilt over to eg cut a 45 degree slope into a piece of wood, when the saw is tilted over it can't cut as thick a piece of wood. If the saw blade sticks out 64mm tilting it over to 45 degrees means it might make it through a 40mm piece of wood
The blue is the wood, approx 100mm thick. The diagram represents the side view of the wood after it has had slots cut in it at 90 and at 45
You're trimming 30mm off the bottom of a door; you'll be trimming at 90 degrees on the wood, which will probably be marked as 0 degrees on the saw. If you haven't bought a track you can clamp a straight edge to the door such that the edge plate of the saw is guided by it. You'll need to measure the distance from the edge of the saw blade to the edge of the plate on the saw and add this distance onto 30mm and clamp the guide at that distance.
For instance, my evolution circle saw has a square plate that can be tilted and the edge of the saw blade tooth is 31mm from the edge of the plate. I would clamp a spirit level at 61mm from the bottom of the door and then spin the saw up and just cut a tiny nick in the door and measure again to check it really was 30mm, make any adjustments necessary to the guide rail (spirit level) and run the cut
As you're cutting a decorative surface I would recommend you either do a first pass cut very shallow like 4mm, then cut all through, or I would clamp another piece of sacrificial flat wood to the door and cut through both of them. This will help prevent the door face from splintering and leaving a messy cut edge;
a circ saw cuts upwards toward the plate on the saw. The bottom face of the wood is fine because the decorative surface of the wood is supported by the thickness of the door, but the top face that the saw is running along has no support to stop the top face from splintering upwards as the saw teeth exit from the cut. A supporting wood helps prevent this, as does cutting a shallow pass. With the shallow pass route you can also tap the guide rail down towards the bottom of the door to move it a fraction, maybe half a mm, so that if the blade vibrates as it cuts it doesn't hit the side of the shallow cut