Why do most pick-up lines fail?
Because they could be sent to anyone, and the person reading knows it. The lines that work point at something specific, are easy to answer and do not take themselves too seriously. That is why the most useful thing you can type is one detail from their profile.
Does the app matter?
It changes the norms. Hinge rewards replying to a specific prompt, Tinder openers can be lighter and quicker, Bumble openers carry the whole first impression, and an Instagram DM needs a reason you are messaging at all. Choose the app and the line is written for it.
Funny, smooth or bold?
Style sets the vibe. Funny is the safest with someone you have never spoken to. Smooth works when the profile is flirty. Bold works best when you are confident it will land. If unsure, start funny and let them set the temperature.
What comes after the opener?
Other tools take over. Conversation starter from profile writes from a profile screenshot, Reply to a text handles whatever they send back, Add rizz upgrades a reply you already wrote, and Is this flirting? helps when you can't read their answer.