It’s part of the Lucasfilm canon, yes! It’s from the Scum and Villainy in-universe book (as in, it’s written from the perspective of the Divo family, that cop Tan Divo we saw in The Clone Wars) book, where Mace argued for leniency with Boba and the Judiciary branch was like “lol fuck no”:
[Star Wars: Scum and Villainy: Case Files on the Galaxy’s Most Notorious]
ANYWAY MACE WINDU DID NOT SEND BOBA TO ADULT JAIL, HE ARGUED FOR LENIENCY AND REHABILITATION INSTEAD, WE STAN MACE WINDU ON THIS BLOG
Oh I never knew this. This is really interesting to know actually.