The transition from Batman: The Animated Series to The New Batman Adventures brought many changes, sparking debate about whether these shows are distinct or continuations of the same storyline. Both series are set in the DC Animated Universe (DCAU), but they diverge in art style, tone, and character development, with TNBA being the more modernized of the two. Though ostensibly a sequel to Batman: TAS, The New Batman Adventures was notably different, prompting many to consider them separate shows.

https://screenrant.com/batman-the-animated-series-new-adventures-biggest-differences/