Saito provides some insights with his comment on Bocchi's final ep in the official guidebook. Particularly with this final line of the season being the defining line of the show:
Despite all the changes Bocchi went through this season, it was never his interest as the director to try to "fix" Bocchi or completely revert the loneliness she felt in all those days in her closet. That loneliness is the core part to which he felt connected to Bocchi, so despite the growth we see and the new connections she's made, that loneliness will never fade away completely. Kirara fans are acquainted with the bright and relentlessly cheerful depictions of friendship that K-On defined, but even in that show, it was often met with moments of extreme melancholy and transience—levels of genuine poignance that many of its derivatives failed (or haven't even tried) to capture. Saito said that solely depicting that cheerfulness we associate with Kirara is simple, but with nothing underneath that cheerfulness to contrast against it, makes the work subsequently feel shallow to the audience. So even with sequences like this, with Bocchi contently walking with her new band, Saito knows that that's only one side of her, and by accepting her gloomy side just as much as her cool "guitarhero" side, just like the rest of Kessoku Band does, that's immediately way more validating (and interesting) than the alternative that we normally see.
And so, Bocchi's everyday routine continues on like normal, and with the season's final shot, Saito sought to capture a neutral look into Bocchi's psyche. One side of her is her newfound side, the one she's facing towards as she walks to STARRY: the side where the sunset lies, and where the lamp post stands (remember that lamp posts were used as a symbol of her growth in episode six? fucking GENIUS). And the other is the side she's facing away from: the gloomy side of her that still hides in the shadows—undoubtedly brighter than before as a result of these changes, but still a side of her she'll return to at the end of every day. This particular idea in depicting mental health isn't anything new, but this level of genuineness isn't something you see everyday, and in such an ambitious show no less—unequivocally kirara yet always striving to do something more & unique; it really is my dream show 🥲