Yeah, that depends entirely on the company and – most importantly – you current boss. Also, I don't think ADHD is a protected class so, even if accommodations are made, the next boss that comes over can totally do the PIP thing.
For anyone reading this: if you ever find yourself placed in a "PIP", leave. That's like being inside a black hole's event horizon, you'll never come back.
You can in fact refuse a PIP. I don't mean refuse to sign the paper they give you, I mean refuse the whole process. This will almost certainly result in the termination of your employment, but depending on the circumstances you may get far better terms than simply being let go.
That said, I have seen people come back from a PIP and kill it, to the point where on their next review they get all of the equity they lost in the prior cycle plus the comp from the new cycle. Obviously this is rare, but I have seen it.
For anyone reading this: if you ever find yourself placed in a "PIP", leave. That's like being inside a black hole's event horizon, you'll never come back.