currently there is no native walk+talk animation. You have to create a new outfit for the character where his mouth moves when walking or a new animation index in the existing outfits walk animation and change to it to get talking animation.
Also you need to use narration text or use the character background text (background text untested because i dont know if the text gets then interrupted because the char walks).
has to be narration text mate as display text background or regular triggers the talk animation of the character. If you click a new destination then it should walk, but I've no idea if the character will get interrupted & stop to trigger the talk animation on new display text. Either way, narration or object text would be recommended in this case depending on how you need it to work.
As for Maniac Mansion, I doubt they had native animation support for walking & talking at the same time either. The older pixel games tended to create tons of animation variations for every single thing unlike these days where most point & click developers seem to think generic animations are enough.
Maybe it's something that could be added to the engine in the future, but who knows? I believe it's something that could be achieved very easily using sprite part animations. Currently we have Spine support, but it's a bit too expensive for most of us, but not to worry as Simon is working on adding support for at least 3 other sprite part runtimes for Spriter, Dragonbones & Creature, all of which are really cheap or even free. Hopefully with those he will work on adding better support for runtime functions so we can swap out various spriteparts while the game is running, which would allow you to have you character blink, talk, perform facial expressions or change clothing, etc.