It’s the “Democrats” party, a right/center-right one. DEM = Democrats.
Don’t like them at all but they’re better alternative than far-right Bolsonaro candidates or candidates from the “Republicanos” party (like Crivella or Russomanno) who focus way too much on religion and like to appeal to evangelical voters.
In that sense, DEM is replacing these more radical and dumber sectors of the right, which is good. I would rather have DEM canalize the strength of the right like PSDB used to do, since they’re more moderate in comparison to this right that emerged in 2016/2018.
Hell, the Rio left hates Eduardo Paes (DEM), but we’ll definitely support him against Crivella (Rep).
What are the demographic/ideological differences between Democrats and PSDB?
Although the difference isn't hugely important now, the Dems come from the old military regime party ARENA (or more accurately, a liberal wing splitting from ARENA's legal successor party formed the Democrats as an attempt to create a democratic Right); while PSDB were born from legitimate opponents of the military regime. In terms of demographic differences, the difference was normally that PSDB did very well in Sao Paulo and badly in Rio iirc.