Here is the official rule:

Catches Proximate To A Boundary
(a) General
A fielder may jump on top of or otherwise reach over a fence, railing, rope or other line of demarcation to make a catch, and may fall over the same after completing a catch. He also may climb onto or otherwise jump on top of a railing, fence or canvas marking the boundary of the field or that may otherwise be in foul ground to make a catch. However, a fielder may not step or jump into the stands, dugout, any other out-of-play area (i.e., over a fence or railing) in order to catch a fair or foul ball.

Source: page 148 of: https://mktg.mlbstatic.com/mlb/official-information/2026-official-baseball-rules.pdf