Website not indexed by Googlebot – problem with http header or sitemap or robots

Hi guys!
I have a problem with my website and I would like to get help.
Two weeks ago my web hosting changed its servers and I have had several problems since then. What I can’t solve is about indexing the website through Google Seach Console.
Before the server change, I hadn’t done any seo to my website, but it was anyway on the first page in the searches because its previous version, the old website, which was not in wordpress but in html, written manually line by line, had a 93/100 seo score. Since the situation was good, I had postponed, with the new wordpress site, the seo work but the change of the server has forced me to face the problem. A friend recommended Rank Math and I think it’s a great tool. Currently the mobile version of my website is on the first page, in the very first place in the Google searches, but the desktop version is totally absent. It is present on Google but not indexed because I reported the url but it does not appear anywhere.
The sitemap, both the one created with Rank Math and the one I’ve created manually, have been rejected by Google Search Console for a general HTTP error: 403 error. Some tests reported an error in the robots.txt file or in the robots meta tag, maybe there is a command conflict or access/permission problem. I am attaching the screenshots of some header checkers tests I made and the settings I have in Rank Math. I’ve also tried to do a Googlebot simulation following this article ( https://gentofsearch.com/blog/chrome-googlebot-simulator/ ), and while other robots including Googlebot Mobile and Googlebot Desktop upload the website without any problem, Googlebot gives a 404 error on all resources and doesn’t show the webpage. Apparently Googlebot can’t access to the folders wp_content and wp_includes In some forum it is said to delete the line Disallow: / wp_content / and Disallow: / wp_includes / from the robots.txt file and replace them with Noindex, but it doesn’t work. Just to leave nothing to chance, I have to tell you that I’ve also these plugins: Easy WP SMTP, Elementor, Element Pack Lite – Addon for Elementor, Elementor PRO, Site Kit by Google and WP-Optimize – Clean, Compress, Cache. Maybe any of them could give problems? Anyone have any idea what the real problem is and how I can fix it?
It is really frustrating because the internet is my only sales channel as my clients are international. Traffic has decreased from 14K to 1,4 and the number of inquires is almost zero, while they were 2-3 per day until a month ago. I really need help with this, I feel like I haven’t enough knowledge for solving the problem on my own.
Thanks a lot to anyone who can provide any clarification or advice.