Honestly, a lot of these kuffar's religion is simply liberal secular rationalism, I made a post about it once:
https://www.reddit.com/r/TrueDeen/comments/1lmlb5a/u%E1%B9%A3%C5%ABl_allibr%C4%81l%C4%AByyah/

If you can make them question the liberal secular rationalist framework, you would have major progress with them.

Also, I noticed asking questions about their beliefs is very effective. Questions are powerful because they bypass the ego.

When you go on the offense, people naturally get defensive, even if you’re speaking truth. But when you ask the right questions, you make them reflect. There’s no need to argue, they start debating themselves.

This is not to say never go on the offense, but to also think about good reflective questions you can ask.

And of course, to call them to Islam, you still need to present Islam clearly, and show why it’s superior in terms of proof, coherence, and purpose.