I was thinking the same. But I personally would ask for full immunity if there was any chance at all that the prosecution could use something I say against me. His lawyer will counsel him and he should take his lawyer's advice.
Part of his plea deal was that he would have to testify truthfully at any subsequent trial. So I don't think he can take the Fifth. And he basically has immunity unless he lies.
But maybe he could he just say that he no longer remembers certain details. I wouldn't have thought so, but based on his recent actions as laid out in the court filings, who knows?
Here's the filing I'm referring to: https://api.realfile.rtsclients.com/PublicFiles/f176abc1e5724236a069e99a176a74d5/34fbfc43-6bb6-4b23-9a33-97a37104152e/Dec%204,%202023%20State's%20Response%20to%20Motion%20to%20Seal%20Certain%20Pleadings%20and%20Documents.pdf