Competitive Niche

Guest Posting is the best way to get backlinks

create valuable content and pay for backlinks from large websites

You need to pay for high authority website backlinks.
Additionally, you can find backlink resources yourself and create backlinks. make sure if the backlink is not indexed on Google then it is worthless so check and push the backlinks for indexing.
You can't do it for free if you want to compete

It's by creating a highly informative and unique piece of content, which when you share on social media can generate backlinks automatically.

It's not easy but it is worth the time. Or you can also directly ask some blog owners for free guest post. Most of the time they will decline but some may acknowledge the effort you have put into your blog.