Thanks for the update and further testing.
So as I understand it, the issue is the fact that the snippet has been manually added not by Site Kit.
At present if you add your Optimize container via Site Kit it will look for a Site Kit inserted snippet to attach the Optimize container ID to. If you don’t have any Analytics snippet added via Site Kit then yes, this can result in the non placement of an Optimize container. We’ve opened a GitHub issue for this. Many thanks for helping us identify this possibility.
Sorry to hear also you’ve had to disable AMP on your site. It may take further configuration for AMP URLs although if you do decide to revisit AMP with Optimize and Site Kit we’d be happy to help where possible.
Google Optimize is only working when Google Tag Manager is disconnected. Is this known/intended?
While typically this isn’t the case if you’ve inserted your Analytics tags via Tag Manager and Site Kit hasn’t inserted any Analytics snippets (within the Analytics module) then there is a possibility that the Optimize snippet will not be added. The placement of an Optimize snippet within Site Kit at present is dependent on the plugin having inserted an Analytics tag on your site (with a Univeral or GA4 tag).
If you’re just using Tag Manager alone without any Analytics tag then this doesn’t impact the Optimize snippet placement or functionality.
Let us know if you have any further questions on the above and we’d be happy to help.