Link Building?!.. I'm lost and need help

Hi
I now have two main sites in the Arab field, and I got more than 199 million visits over 4 years, and I have good experience in writing content and on Page Seo and also Off Page Seo

But unfortunately I neglected the off Page seo and my competitors outperformed me in the search results, I have general experience in off page seo, but I do not have any previous experiences! .. I'm lost and I don't know where to start from

Should I start with the guest post, should I start with web2, should I start with edu, I don't know.. I want to start professional off page seo because this is my weakness.. Please I want help and advice

Here's a guide I, personally, like.
It's easy to follow and no overkill:
https://www.blackhatworld.com/seo/guide-thinking-on-a-link-building-strategy-from-scratch.1398106/
As for the anchors, I use this guide:
https://www.blackhatworld.com/seo/w...build-their-anchor-text-in-backlinks.1118984/

Now, many people will start recommending you from their own personal experiences. For all of us is trial/error/success(in most cases), however, we are not tied to one kind of link-building method nor some magic method that will magically put your website on the first page.

What I personally recommend:

Optimize your content to its fullest - Basically don't let your content dictate the state of your rankings. Most of the time, people think that just by writing random content, they will reach their goal. Unfortunately, no.

Be active on social media related to your website - How does this help? Well, I can't see it helping with the rankings nor with the "off-page" that much, instead it's a source of targeted traffic. Let's call it "social signals" as more people know these things that way.

What kind of link-building you should conduct? Well, that is up to you. Some will recommend PBNs, some will recommend Web 2.0 (which is absurd in my opinion), and some others will say guest posting.

As for a start, I would personally suggest reaching out to other website owners that have similar content to yours. Some of them will want to exchange link for link, some will just want the money - the rest is up to you.

After that, you can slowly increase the amount of link juice that powers your website(I mean backlinks) with other kinds of backlinks. In my own experience, reaching out for guest posting was enough and it directed my website towards the best as it is always a relevant/same niche to mine.

Ahm...

TL;DR

Optimize your content to its fullest.
Guest posts(in your niche/related to your niche) for the win.

Eventually, if your niche is super-mega-ultra competitive, you can appeal to Private Blog Networks(Don't pick random ones. Make sure you're getting into something good, with experience).