First, i target informational and transactional keywords. and the authority raised from 2 to 7 because of the content quality , yes i did internal linking i told you in the post im doing i content hub so it must be internal linking there
I still don't think you can increase authority with content, you must have acquired some backlinks that you're not aware of.
No matter, there are still a few things that are weird / would need more details. Like for example...
1) you said you're working on your content hub and that - as a result of this - you do have internal links. But we don't know how good your content hub is and how good your internal linking is.
Like, are you linking all of the relevant pages, or did you leave some of them out? Because orphaned pages can drag your site down, so it's best to interlink everything.
2) the content hub itself... which keywords does it target, and what is its structure?
Because, from what I know, purely informational sites don't rank as well nowadays, so you gotta have some ecom / store / business stuff attached to your blog or else you might not rank at all and this is weird because if you DO have an ecom / store / business attached to your blog in order to rank you will still want to target informational keywords as those are usually the easiest to rank.
Weird and confusing, I know. But that's where we are....
3) in your initial post you said that you've "tested some medium competition keywords" but tested is very ambiguous here. You've tested HOW? You published articles around a few keywords (and did you include them in your content hub and interlink them properly, or you just published them on the side and checked if they rank?), waited for 1-2 weeks to see if they rank, you noticed that they didn't and then removed the content around those keywords? Or how exactly did you test this?
4) I've heard that trust is a huge ranking factor nowadays, even bigger than backlinks and if this is the case your site probably has no trust with google, which is probably why you're not ranking.
I've no idea how google assesses trust, but I have a feeling that social media is part of it. I could be wrong, of course, but even so, having social media presence as a business might pay off in terms of traffic and trust with google, so if you don't have social media accounts yet on sites like Twitter, Instagram, LinkedIn, etc I think you should get them.... And also build a following on them too, of course, otherwise I don't think it's helping....
5) backlinks can still work, but - especially if your site is fresh - I would focus only on quality backlinks, ie. quality PBNs, quality niche edits, and quality guest posts. You can throw some foundation links in there if you want, just keep it under the radar and focus on quality at first.
6) when you say there are no more low difficulty keywords to target are you confusing long tail keywords with low difficulty keywords? Because, it's true that - most of the times - these 2 are synonyms. But there are also long tail keywords that are brutal to rank for, so when you search for low difficulty keywords don't assume that short keywords (2-4 words long) keywords can't be low difficulty. Probably that most of the time they won't be low difficulty since short keywords tend to have search volume, and search volume usually implies medium to high difficulty, but just analyze the SERPs carefully for every keyword that you feel is a good fit for your site, and don't just trust in the difficulty score that Ahrefs / Semrush gives.
This being said, if there really are no keywords left anymore for you to target (many niches are indeed limited in how many keywords they can use) focus on building your site's authority and trust (ie. get backlinks, work on your site's on-page SEO and social media), and - while you're waiting to get rank - focus on building up the traffic in other ways (reddit, YT, etc).
Also, there might be a google update in the working, so I wouldn't stress about the ranking just yet. Take advantage of the next 1-3 weeks that might still be uncertain to improve your site (internal linking, technical errors, site structure, ease of navigation and crawlability, content optimization and improvement, CWV scores, etc) and if after 3 weeks nothing changes (you still don't get impressions or clicks, or you don't move up the SERPs) it's most likely you are being sandboxed, or your site is too weak and needs more authority (ie. backlinks). Of course, it's possible it might need trust more than backlinks, but I have no idea how to build trust, so work on your site's SEO and social media presence in the meantime...
But like I said, you probably need to have some business / ecommerce component attached to the site as - despite of how much I hate this - google really does favor men in suits and will make the SERPs exclusive to businesses in the near future, so probably the era of purely informational sites (blogs) is over