I did not make any changes recently related to this, but I can't edit or open any products from the Magento admin.
Here is the screenshot for what I see when I try to open a product.
Why am I not able to edit products?
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You can try this:
Using the url from the page you took the screenshot from. It should look something like this:
Then using a known product id and the key above, modify the url like this:
This should let you edit the product if it exists.