Good SEO never ends. I could probably spend an hour just listing the things you could do.
Spy on competitors. What kind of content are they making? Is it being successful? Should you do the same? What kind of links are they getting? Could you get links like that?
How can you improve their EAT? Can you get mentions in authoritative places? Are there parts of the website that perhaps are seen as untrustworthy to users? If so, can you fixed those issues? Can you do a better job of demonstrating your business’ expertise?
Have you read the quality raters Guidelines for clues as to what Google is looking for to see in regards to EAT?
Can you find any external links that are pointing to 404 pages and redirect them to other relevant pages?
Have you looked at pages that didn’t do well with core updates and figured out why?
Have you looked in search console to see which important keywords have dropped rankings and figured out why?
Have you implemented conversion tracking to help measure which marketing efforts are working and how you can tweak them?
Core web vitals are becoming a ranking factor in a few months. Almost Every site I’ve seen needs improvement in this area. You may not have the development skills to implement things, but a good SEO should be able to point out where the issues are and guide a developer on how to fix them.
Have you put together a content strategy based on what is working for your client and what is topical and what your customers want to see? And once you’ve created content have you tweaked your strategy based on how it performed?
Have you analyzed their link profile to determine whether disavowing has the potential to help them?
Have you found ways to get good, authoritative links and mentions?
What you described is just the start of SEO.
Edited to add: I am being a little facetious in this response. If you’re new to SEO then of course you have not done all of the above. It takes a long time to learn SEO as a career. If your employer has tasked you with SEO and you are not quite sure what you are doing beyond ticking some boxes for optimization, and the site is still not doing well, what your employer has tasked you with is something that they may need to hire professional, experienced help for.