In the ending of DS9, Odo went to the changeling homeworld and rejoined the great link and cured them of their disease. And he kinda made them more mellowed out or something like that. In Picard S3, Worf mentions something about how his friend (obviously Odo) sent word it wasn't those changelings involved in the plot. So Odo and all the Gamma quadrant changelings are fine, it's just the ones that were experimented on by Starfleet that we see in Picard S3.