Improve Shopify Store Speed

Shopify-based D2C home decor brand.

Current Google PageSpeed Insights score: 30 on mobile, 50 on desktop
Looking for a real, verifiable improvement in load speed and core vital score on PSI — the deliverable will be checked against live PageSpeed Insights results, not a screenshot
All existing apps must remain installed and fully functional (reviews, chat, upsells, etc.) — no removing or disabling app features
All tracking/analytics scripts (Meta Pixel, Google Analytics, GTM) must continue to work exactly as they do now — these should not be touched
Cart and checkout functionality must not be affected in any way
Work must be done on a duplicate/unpublished theme first — you'll get admin access, and we'll review a preview link before anything is published live

What we need in your proposal:

1. Your minimum target score for mobile and for desktop
2. One specific thing you noticed after actually opening and testing the site
3. A short description of your general approach
4. How much time will you take?