Echoing the sentiments that:
- an actual, prescriptive moral/lesson is not needed so much as just a point in the sense of "why are you telling me this?"
- Nevertheless, everyone has opinions and some of them are going to leak through into their writing no matter what
I do think for a story to keep your attention and not meander around aimlessly, the author does have to have a conscious awareness of "why am I telling them this?" It could be
- a message, like "friendship is important", or
- a theme like "what is the nature of friendship and is it always good? Let's explore from various perspectives", or
- just something like "board games are cool, I'm going to write about characters playing board games because the world is sorely lacking in stories about characters playing board games".
(That is, I think the answer to "why are you telling me this?" needs to be more specific than 'it's cool/silly/fun/cute' - something individual people might find cool/silly/fun/cute/etc like 'board games', or 'baby fantasy animals', or 'enemies-to-lovers romances')
I will dispute the sentiment that "slice-of-life is when no message/point" though. I'd say My Little Pony: Friendship Is Magic is mostly slice of life sans the season premieres/finales when something big and world-shaking happens, and even without those, there's like a friendship lesson in every episode
Unless your definition of 'slice-of-life' means having anything of meaning at all happening pushes the genre into drama or smth ¯\_(ツ)_/¯
In fact, I feel like I'm drawn to writing slice-of-life precisely because it lets me explore deep themes without falling into a simplistic narrative of 'X is the solution' because life kind of just goes on for the characters instead of there being one big dramatic confrontation where the protag has an epiphany about X and uses the power of X to solve things forever and everyone lives happily ever after. Even if I'm clearly pro-X leaning, it feels like I'm not being too preachy, like the message isn't 'X is the solution' but rather 'maybe X is good, actually?'