Hi @angeloarlotta
We are not able to reproduce this issue. We are using WordPress v5.6.1 with Yoast SEO v15.8 with WooCommerce v5.0 on Divi v4.9.
We went to a product page and went to edit it from the front-end. We were able to add modules to it. See image: https://ibb.co/HGRhq5w
We then selected save in the bottom right and the page saved as expected. See image: https://ibb.co/Qr4V5Vx.
We can see in the screenshot provided to us here: https://pasteboard.co/JOmmBSY.jpg that Divi makes mention of the need to try a couple different things such as increasing memory, checking your firewall error log, disabling browser extensions etc.
We understand when Yoast is the only plugin active and you have Divi the issue is happening. We would like some more information.
1. Can you confirm your server has all the right requirements? ?If you are not sure, speak to your host provider.?They may need to increase the PHP memory by doubling or tripling it.?This guide explains more:?https://kb.yoast.com/kb/plugin-requirements/.
2. If you check your firewall error log (like ModSecurity) are they showing false positives which are triggering this result? If you are not how to see the error log or how to examine it your host provider can help.
3. Does the issue still happen if you use a different browser and/or disable any browser extensions?