I’ve written about that over on Ubuntu MATE Discourse, which for now is still operational.
At this point in time I’ve heard of no special treatment for Ubuntu MATE systems in the resolute cycle; thus I’d expect the same as I wrote about on the bionic cycle when Ubuntu Studio 18.04 was released but not as an LTS release.
Of course, the Ubuntu MATE 26.04 may not be released as a new ISO (differing to my Ubuntu Studio 18.04 example); I actually expect that to be the case, but that to me doesn’t actually change anything, as the new ISO is for new installs, and for now Ubuntu MATE is still an official flavor of Ubuntu, thus I still believe what I wrote on an answer here applies
An existing Ubuntu [MATE] 25.10 or Ubuntu [MATE] 24.04 LTS user will be treated as if a Ubuntu 25.10 or 24.04 users by release-upgrade tools, as for now Ubuntu MATE is still an official flavor; and changes [implied?] relate to upcoming ISO release only.
I’m betting you’re after an answer from someone other than me; after all I’ve written many over on the Ubuntu MATE discourse, or just want a discussion on this site?, but I believe I’ve tried to accurately describe what will happen with currently available information.