is choosing keywords for seo still worth the effort?

yes, but the job has changed. you pick the topic and the intent behind it, then one page covers all the ways people phrase it, rather than one page per keyword. what still matters most is looking at what already ranks - if page one is all big brands or all videos, a blog post from you probably isn't getting in, and it's better to know that before you write it.

There's a manual route and it's a decent one. Start in Search Console - the queries you already get impressions for but sit low on are the cheapest wins you'll find, because the site is half-ranking for them already. Then autocomplete, the related searches at the bottom of the results page, and the questions block. Last, read the page titles of whoever ranks top three for your main term. That gets you most of what a paid tool gives, minus the volume numbers.