I'm 59 years old, 6'6" with 36" inseam, I presently have a carbon Teschner road bike. looking for at either a gravel bike or hybrid bike I have not decided yet, but my main concern is getting the correct size.
In normal times, I would advise you to visit a bike shop and get fitted by the staff. Of course, these are not normal times. It would still be worth talking on the phone to a local shop and seeing what they can do for you and what they'd recommend.
It sounds like you've got a long torso. This can be accommodated by seat setback, stem length, and handlebar reach, although those will affect other aspects of your fit and the bike's handling.
If there are specific bikes you're interested, check the manufacturers' websites to see what their fitting guidance is. There are some bike manufacturers that direct-ship to consumers (and more are doing so during the C19 crisis). They usually don't build to order to accommodate fit, although I've seen one or two that do.
Road and gravel bikes are sized by what you might call the virtual seat-tube length (I think hybrids are the same, but less sure). This is the distance from the center of the bottom bracket to a point extrapolated from the seat tube where it intersects a horizontal line extended from the top of the head tube (this is a throwback to when bikes had horizontal top tubes). And usually, the seat-tube length will be ⅔ your inseam; hybrids will probably express this in inches and gravel bikes probably in cm. So you'd probably take a 60/61 cm bike (frames are mostly sized in even-numbered increments), which is big.