Updating Helix3 framework remove this problem.
Extensions: Update > click "Clear cache" button (top left)
Click "Find updates" button
Mark all plugins with "helix3" name
Click "Update" to install new versions
Source:
1) https://www.joomshaper.com/forums/menu-not-working-error-500-after-installing-joomla-3-8-10
2) https://www.joomshaper.com/documentation/helix-framework/helix3#how-to-update-helix3
