Hi Grumpy
Any volume over 150 will be fine for your weight.... but IMO, width is the key to comfort when first learning, especially if you have no previous surf experience.
I would advise a minimum of 32" wide, but don't be afraid of going wider.... yeah, I know many here think wide is bad, but they are young and fit with a load of surf experience. My 11 year journey on SUP surfboards has proven to me that width is super important.
At 6'1 you are on the tall side, which raises your center of gravity, so 33 to 34" wide would ease the learning curve.
At 73, I am a Sunova team rider and marketer, so from our line, the board size to look at would be the ONE 10'2 x 33 at 184 liters.
Flat enough rocker to paddle extremely well, good length and width to learn on, and lightweight. Not a high performance board but it surfs just fine in small waves.
No matter what you get, there is going to be a humbling period at the start, but with the right board you will soon get past the awkward stage.
I began on a 36" wide Starboard Avanti that was 11'2 and 230 liters. Great board for BIG folks (I was 130 kg at the time)
Lifelong surfer..... I fell 100 times my first day

But that quickly passed, and I was on my way into the magical world of SUP!
Lots of good choices out there, enjoy your journey into a new surf life!

This guy (about your size) bought the 10'2 ONE after his first paddle session on it.... he had never surfed in his life.
Now he is chasing surf all over Florida and loving his new surf life
I surfed with him last week!!! He loves his ONE!