Only homepage is indexed and service pages are not.

The site has good internal, external links and has good score on lighthouse. Website had a history of 503 errors(recently fixed), low domain authority, no blogs, no about page. And robots.txt file had some caching issues(recently fixed and submitted a new one). GSC just shows that page can be indexed after using the inspection tool. What additional steps can I take to make sure those service pages get indexed. Thanks in advance, this sub has been very helpful. Happy new year!!