Not directly in TNG
In ConundrumConundrum, we see:
Dr. Beverly Crusher tending to Kristin, a crewmember injured cliff-diving on the holodeck
that holodeck program was Holodeck Program 47-CHolodeck Program 47-C. So, although we don't observe it in TNG, we assume that in TNG the holodek could manipulate gravity with this program, otherwise Kristin would've fallen straight to the ground! She must have been suspended for a period of time before the jump ended.
In VOY though we do see gravity in operation in Extreme RiskExtreme Risk:
On board an orbital shuttle, B'Elanna Torres is preparing for orbital skydiving in the holodeck...[later she] jump[s] out of the shuttle...
So, in order for Torres to accomplish that jump without jumping right onto the floor of the holodeck, the gravity in the holodeck must have been altered.
So, yes, we do see the holodeck manipulate gravity, but not in TNG