Do no-follow backlinks from Quora and Pinterest help with SEO?
The article that rproffitt linked to on SEMrush seems to indicate that the only use case for nofollow links are paid ads. That's simply not true. Nofollow was Google's recommended method anytime you were linking to content that you could not vouch for. While paid ads definitely fell under that category, so did links within user generated content, such as forums. All of the links within member posts have always been nofollow'ed.
As pointed out in that article, lots and lots of links on the web have been nofollow'ed, and Google still looked at them, sometimes.
Well, now it's official. Google has announced last month that the nofollow attribute will now be seen only as a hint. Of course, many SEOs have suspected this for quite some time, but it's now not only officially on the record, but Google is actually encouraging two additional link attributes to replace nofollow as well. In an effort to better understand a website's motives for using nofollow, they are adding two additional link attributes, ugc for user-generated content, and sponsored for paid ads. The original nofollow is now a catchall to be used when you don't necessarily vouch for or trust the content you're linking to, but it doesn't fall into either of the other two categories. It's now at Google's discretion whether and to what extent they will count that as a backlink within their rankings.
In 30 days everyone is out of date on almost any Google subject?
For sure!! SEO is an incredibly fast-paced industry. That's why there are so many questions such as, "What's the best method for <blah> in 2019?" and "What's the best method for <blah> in October 2019?" with the same question asked every few months. Because the answer can be very different!
There are over 300 Google algorithms released every year, meaning there's an algorithm change almost every day. Of those, there are about two a month that are impactful enough to be announced by Google to the SEO community. The SEO community then scurries to make changes. Rinse and repeat.