The numbers are released by Ukrainian armed forces, so it may be biased, but in general they seem to be accepted at least as a good estimation on what's going on.
I think we should all be assuming that these are not real figures. I support Ukraine but would never actually believe these numbers. Disinformation is a weapon of war
Well, they're not that far off from the estimations i.e. USA has given, so while they're absolutely optimistic and/or at the higher end of the estimation they're not just pulled out of stetson either.