Bought a domain, it had content years back. Built a new site. Now its not getting indexed after a few months. Whats wrong?

Hi, what could be done to make the website go into index? Its just not able to index the website. The old site has pages dating back to 2014 and recently 2019 and think even 2023. Problem is, made a totally new website, but its not getting anything indexed. No manual penalty on google search console. Been waiting for 3 months now. Nothing. Tried semrush and ahrefs site tool audits and tried to fix all problems. Any help?