Please, resolve my doubt. Here the word maji has two clearly distinct pronunciations: https://forvo.com/word/sw/maji/#sw One has j as [j] and another as [dʒ]. I've heard it multiple times on forvo in other words as well. Are there two possible pronunciations? Maybe it is a dialect issue? Or whatever else?
The way Dinah pronounces it is not with [j] but with [ɟ] (https://en.wikipedia.org/wiki/Voiced_palatal_stop). The "official" pronunciation of <j> in Swahili is with either [ɟ] or, rather, a weakly implosive version of it: [ʄ] (https://en.wikipedia.org/wiki/Voiced_palatal_implosive).
If you go into the western areas where Swahili is spoken, such as in the Eastern D.R. Congo, you might hear it pronounced with [j] and see it spelt mayi.
[dʒ] is a common non-native pronunciation that doesn't cause any problems. Pronounce it whichever way you like the sound of or feel comfortable with. There are no minimal pairs - no word depends on making this distinction - so it's really up to how native you want your accent to be.