You might be too young to remember Ally McBeal but her boss on the show would fake smile for the very same reason. It was comedic but it really does have an impact. I think it’s fine sometimes to just not smile and to look serious or have RBF some days. Hell, its nobody’s business but your own! But it really does not work out that well for you EVERY day. We all have to just keep on keepin on and we are all suffering in varying degrees at various times. All of us. So your smile will absolutely change someone’s day, if its authentic and empathetic. I loathe those fake polite smiles that don’t even see me or use the eyes in a real way, you know the ones but as soon as someone connects with me through eye contact and some kind of warmth, it really completely changes my day. I hope the best for you. Stay strong.