I recall a report from ASPI that said it could fly 4000km with more payload than F-35. As far as I can find online most people/reports/websites say estimated ferry range in the range of 5000nmi.
Just read that report. Authors say 4000 km is a very conservative estimate based on b2 public figure of 11000 ferry range.
Aspi is just a think tank with no special info access and I've found at least one instance where one of reports authors mentions 5000+ km radius estimate for b-21, in another aspi article.
Basically , b-21 radius is unknown but personally, I would be surprised if it was under 5000 km. That's because b-21 isn't meaningfully smaller than b2. For somewhat smaller wingspan, it's also lighter and likely has more efficient engines. I wouldn't be surprised if it matches b2 radius figure completely. (At half the combat payload though)
And even that might be very conservative figure. When b2 was made, it's perfectly plausible b52 range (14 000 km with payload, 16 000 km empty) was somewhat of a target. Approximately 6000 NM stated at AF website could very well be deliberate simolification. If so, I would put both b2 and b21 combat radius at 5000 to 7000 km, depending on the actual payload.
Sadly, no think tank really has any more accurate data or estimates than people on forums can conjure up.