There really aren't any must-read books, except for certain areas there are a bunch of must-read books, and none of them make a good entry point to the study and practice of philosophy.

Like most mature fields, philosophy has a well developed body of theory, and jargon for discussing it, and understanding it often requires a decent knowledge of the history of philosophy (most philosophy is done in reaction to earlier philosophy). The person here suggesting Heidegger's Being and Time is suggesting the equivalent of "try doing brain surgery" to someone thinking about learning more about medicine. It's literally one of the hardest texts to even start, let alone understand.

From your question I get the feeling that you're not looking to gain academic expertise in philosophy so much as general understanding and practical application to your life. So, here's a suggested list of things to try and see which seem accessible and applicable to you:

1. Listen to the podcast A History Of Philosophy Without Any Gaps [0]. It's an excellent high level survey of the history of philosophy that does a good job making the very abstract ideas concrete and applicable, without getting into the weeds. It's also a gentle introduction to the jargon.

2. Take a university course on contemporary moral issues. Every philosophy dept in North America runs this course regularly as one of the best hooks into the field for students. It directly takes current issues like abortion, pornography, climate change, etc. and discusses them in terms of moral philosophy, introducing the key concepts along the way. I have a friend teaching philosophy whose central work now is on the moral issues surrounding sex with robots [1].

3. Read Zen and the Art of Motorcyle Maintenance. This book is not very good philosophy, or as an introduction to Zen or motorcycle maintenance, for that matter. But I read it in my teens and fell in love with what the author does, namely thinking really hard and rigourously about his life, his circumstances, and his place in the universe, and walking through all that thinking in a pretty clear and compelling way. It doesn't help with philosophical knowledge much, but it's an excellent depiction of the mindset that pursues philosophy, questioning and reasoning about everything.

4. Read some Plato. His works are small and topical, the dialog form is very accessible, the Socratic method is a great application of rigourous thinking and analysis, and you're definitely dealing with some of the foundational ideas in philosophy that keep recurring in various ways. The list at https://phuulishfellow.wordpress.com/2019/08/18/a-platonic-r... is a pretty good reading order, but read only as far as Plato holds your interest.

For more advanced stuff that's also contemporary here's a list of some essays or books that are well-written, fairly important in their area, and raise interesting questions:

* Descarte's Meditations [2] is frequently used as an accessible introductory text

* Thomas Nagel's What Is It Like to Be a Bat? [3] (someone else mentioned this as well)

* Derek Parfit's Reasons and Persons [4], especially section 3 where he discusses what constitutes personal identity in the context of Star Trek style transporters.

* W.V.O Quine's Two Dogmas of Empiricism [5], on truth and logical positivism

I did a BA Honours in philosophy and it was life changing only insfar as I spent those years reading, writing and analyzing. It screwed my head on very tightly. I didn't have strong opinions on most philosophical topics coming out of the degree, but I felt very much equipped to read and understand philosophy and apply it to my life.

[0] https://historyofphilosophy.net/

[1] https://mitpress.mit.edu/books/robot-sex

[2] https://en.wikipedia.org/wiki/Meditations_on_First_Philosoph...

[3] https://en.wikipedia.org/wiki/What_Is_It_Like_to_Be_a_Bat%3F

[4] https://en.wikipedia.org/wiki/Reasons_and_Persons

[5] https://en.wikipedia.org/wiki/Two_Dogmas_of_Empiricism