Can Stunned creatures contest a grapple?

[TheUser]

My initial knee jerk response is -no- since they cannot act or react, it stands to reason they cannot contest a grapple but RAW doesn't seem to say this. Only that they cannot take actions or reactions (of which contesting a grapple is neither). But the idea is that if it couldn't realistically engage in a grapple, how does it prevent one?

Am I wrong to think a stunned creature couldn't stop a grapple attempt?

[Lunali]

They also auto fail str and dex saves, but apparently can still succeed on str and dex checks so as far as I can see they can contest a grapple, meaning the grappler fails to grapple them in a way that would prevent them from moving.

[Malifice]

Officially it's up to the DM:

https://www.sageadvice.eu/2014/11/06/stunned-creature-ability/

But it appears as if they generally should auto-fail (being incapacitated) or at the least have disadvantage (or the attacker gets advantage).

Consider a BM Fighter can use tripping strike to shove them and that is automatically succesful (it is resisted with a saving throw, which you auto fail when stunned). For a normal shove attempt it's an opposed ability check instead.

You might want to have things like BM manouvers be special (auto succeed vs stunned creatures) and have 'normal' combat manouvers resistable with a check at disadvatage or something.

Its up to the individual DM.