Drop in sales after migration magento to shopify

My website was migrated from Magento to Shopify about 8 months ago and it has nearly killed my business. The drop in sales has been devastating.

The developer assured me everything was OK, but clearly something has gone very wrong. Google Search Console and Google Analytics were only set up after the migration, so I don't have the information from before the move. I need somebody who can find historical data from other sources and work out what happened to my Google rankings and overall performance before and after the migration.

I also changed all my product descriptions and images during the move. The branding and products stayed the same, but I rewrote the descriptions and changed the images.

There are also two parts to the business under the same website: an established e-commerce business and a separate retreat/travel side. They are connected, but I'm not sure the website is structured in the best way for Google.

The developer also put the retreat information into a blog-style page, which I don't think looks professional. I'm not sure whether it should be a standalone page, a separate section or even a subdomain.

I need somebody to look at the whole situation and work out why my sales have dropped so drastically, including investigating historical information from before the migration.

Is this something you could help me with?