I noticed in search console that Google STILL crawls and finds 404 the old .html pages on the site.
The site had such URL's ending on .html some time ago, most of them were redirected. Current site has no URLs ending in .html
However google is still crawling some .html pages and finding 404. I don't know where google is getting those links from. They are not in sitemap, not on the site and not in google index
What are those pages?
You can do 301's redirects from the old site structure to the new Shopify store: https://help.shopify.com/en/manual/online-store/os/menus-and-links/url-redirect