Determining WLB before applying and interviewing?

When you're interviewing for a new company, it is very difficult to get signal on this as you have limited visibility. You can use online resources like Glassdoor, Reddit, and Blind, but the veracity of those is quite dubious. You can try asking them directly, but the better option is often times to ask a more roundabout question (like about deadline culture). You can see the exact question I personally use here: "How possible is it to spot red flags about toxic culture during the interview?"

I am also not a fan of trying to pin an entire company to a certain level of WLB, because as you mentioned, different teams/orgs have different cultures. This is especially true at massive company like FAANG which have thousands of teams. A ton of engineers at Amazon have horrible WLB, but I know many who have very solid WLB there. Most engineers at Meta are stretched too thin, but I was personally able to be a high-performing tech lead there working 35-40 hour weeks.

When you're switching teams internally though, it is incredibly easy to figure this out. Look at the team members' pull requests and see when people are submitting them and leaving comments. If they happen late at night or over the weekend (make sure to factor the timezone they're in), the team obviously has poor WLB.

That being said, WLB is also largely determined by your own ability to maintain rapport with your manager, prioritize aggressively, set boundaries, be productive in general, and of course, have a healthy mentality around all of this (and more). More advice on how to do all that here: [Taro Top 10] Work-Life Balance