Hello,
I no longer have the navigation option in the online store section:
I also have a problem on my website, when I go to the menu, the page disappears when I try to go to the mega menu (red recrangle).
Please help 
Topic summary
Main topic: Two issues with Shopify’s Online Store—missing Navigation in the admin and a front-end mega menu causing the page to disappear.
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Admin change: The “Navigation” option has been relocated. It’s now found under Admin > Content > Menus. This addresses the first problem (missing option in the Online Store section).
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Front-end issue: On the website, opening the menu and moving toward the mega menu area causes the page to disappear. No fix or troubleshooting steps have been provided yet.
Context notes: Screenshots illustrate the absent admin option and the red-highlighted mega menu area where the problem occurs.
Status: Partially resolved. The admin-location issue is clarified; the mega menu behavior remains unresolved and needs further investigation.
