It's a series of trade offs, both can be made to work reasonably well.
I think the first step would be to understand what people search for. Are the variants variants going to be long-tail search targets? Or are people are only searching for the primary products? Keyword research tools can help here. If there is no long-tail variant organic search volume to target, then you're trying to fix a problem that doesn't exist in your case, so just do what's easier.
On the other hand, if there is likely to be organic traffic potential in the long tail in your category, then spend more time here.
For now I've tried to list out a few pros/cons of each approach off the top of my head:
Variant URLs - pros:
Variant URLs - cons:
Unique handles - pros:
Unique handles - cons:
There are probably better people who can consult on a better approach to these kind of scale problems. Might be worth exploring how other Shopify sites are handling similar scenarios, or even reaching out to store owners in similar situations. Personally I'm more used to smaller scale sites sub-1k products.
In general, search engine optimization can improve your site and save time. You just need to know how to do it right. I had my own website, and I hired experts in the business. They analyzed the content and structure of my site, helped with good content creation, and created a keyword that put the site forward. Later I found the site https://limitlessreferrals.info/seo-tools/ and realized that I was free to promote my site without specialists. I advise you to delve into this topic too, learn all the tools and components, and you will understand how to use all its features and tools. I wish you good luck in promoting it.
@sarah_k_BVA not easily. You could use a combination of custom liquid and a metafield with custom liquid to have custom unique Then you still need to make the variants crawlable, indexable (not canonicalized to primary PDP) and uniquie enough in other ways to even get indexed/ranked. Then the URLs are still a mess with variant IDs appended. Or you could use JS for some of this, and do it on the front-end, though I feel this is likely not as robust for the intended purpose of changing what shows up in Google, because even with full Chrome/Googlebot rendering will sometimes have gbot rendering issues and delays the static content can still wind up in the index.