Hi there
When you have these issues, you have options. For instance, if the product is never coming back, you could redirect the page to a relevant product or category, remove the page from your sitemap, and change internal links, or simply create a custom 404 page.
But, if the product is coming back and temporarily unavailable, you could create an out of stock message to let users know the product isn't available at the moment (and will be back) but there's a whole site to explore and check out other products. But again, you have to keep the user in mind with errors on your site.
You can read more about Domain Authority here - although it's not directly stated, I am sure having errors all over you site (especially almost 10% of it) could be bad for it - although it's not at the point right now.
I would start there - what products are legitimately gone? What ones are just out of stock? Can you redirect these to their categories? Are users landing on these pages a lot?
I would also take a look at your backlink profile in Majestic and see which links are worth correcting or removing.
This is upto you to prioritize these issues and remedy accordingly. Good luck!