Question about multiple Limbs and Grappling

[Bruh_moment]

For example, If a Thri-Kreen grappled a human with all 4 arms do the arms grant the Thri-Kreen a bonus to grapple the man?

[Kayblis]

If the statblock doesn't have an entry that nots it gains a bonus to grapple, no. There are no basic rules that states more arms give you a bonus.

This is different from the rules that state that a creature with more than two legs gains a +4 to resist Trip/Bullrush attempts.

[Thurbane]

The DM might feel free to assign a "favorable circumstance" bonus of +2. Strictly speaking. this is recommended for skill and ability checks (DMG p.30) - but I can't see the harm in applying it to a grapple check.

[PoeticallyPsyco]

Having extra arms does provide a concrete advantage, but only if you're using the "grab with just one limb" option of grappling (-20 penalty on the grapple checks without (Greater) Multigrab). This means you're not considered grappled yourself, and having those extra limbs available then becomes really noticeable; for instance, a Thri-Kreen could grapple 3 additional people, or attack 3 times with a weapon held in each extra hand.

Side Note: one of the best grappling options in the game, the Girallon Arms soulmeld, can actually give you extra arms. So while having extra arms doesn't necessarily make you better at grappling, being better at grappling can make you have extra arms.