You can't use Google Optimize (or any other on-page based A/B testing frameworks) to do A/B testing for SEO. A/B testing for SEO has to be done in a fundamentally different way.
A/B testing for users
For users, you can change a page such that some users get one version and other users get the other version. Then you can compare which group of users did better against some metric for increased engagement.
A/B testing for SEO
For SEO, putting two variations on a page doesn't work. Googlebot may only download the page every couple weeks. It will only see one variation at a time. It will index just a single version and show snippets from that single version to all users in the search engine.
If you have a large number of similar pages, you can instead change titles on half your pages while leaving the other half of pages alone. Then you can measure which set of pages does better against an SEO metric such as:
- Googlebot crawl rate
- Click through rate (CTR) as reported in Google Search Console
- Search engine rankings
- Search engine referrals
If you don't have a large number of pages, you will need to try your changes in turn. This can lead to long testing cycles because for each variation, you usually need to wait about 2 weeks for Google to pick up the changes and then several more weeks to gather data.
Google Optimize and other A/B testing frameworks are designed only for A/B tests on users. They don't support the types of changes needed to measure SEO. When I've done A/B testing for SEO, I've always coded the changes into my site on the backend.