It really depends on the topic (probably not for Linux), but Medium seems today the best option if your goal is to earn money.
My last 2 articles in Medium generated $500 and +$800 (and growing) for a total effort of around ~6 writing hours per article, so I think it is a very viable way to make a living writing 100% online.
Sure. Medium paywall works surprisingly well. You simply need to publish your article and activate Medium paywall after a very simple KYC.
The point is that if you don't have an audience/publication, no one will find your article. That's why it is usually better to publish your content under a publication focused in the same topic than your article. If you are lucky, Medium will also promote the article in their newsletter and in Medium homepage and visits will boost.
Then Medium pays you a fee based on the article performance. It is not clear what parameters they consider to calculate the fee, but it seems to be a mix between views and reader time.
Based on my limited experience, they key metric, apart from views, is the total reading time. If the article is short but has lot of visits, revenues will be low.
As a writer, you simply need to sign up for Medium Partner Program (and complete the KYC sending your ID, bank account details, etc.). They pay quite well (the first week of each month).
Medium gets revenues from premium users who pay $5 per month and distributes all the revenues based on views, reading time, etc.
My last 2 articles in Medium generated $500 and +$800 (and growing) for a total effort of around ~6 writing hours per article, so I think it is a very viable way to make a living writing 100% online.