Bounce rate went from 30% (old site) to 80%(new site) - why?

Hi all,

This site has been killing me the last few months. I'm trying to understand why the bounce rate is so high compared to the previous site the client was using. Here is what's been done:

• Revamped site
• Added in new pages and blog posts
• Using SEO tools (RankMath) to make sure meta descriptions, alt tags, etc is working
• Making sure content is relevant
• Doing paid LinkedIn/Google Ads
• Site is slow but working on fixing that
• Monitoring the site with Search Console (few pages marked as no-index for some reason, but trying to fix that too)

Thought I was doing a good thing with the site, making it look better etc, but seems like I only made it worse :/ No idea what could be causing such a high ramp in the bounce rate.