Hi @JewelryNest,
Your theme is using some reference (into the layout definition) that isn't valid.
As the message says:
Element 'referenceContainer': This element is not expected. Expected is one of ( action, arguments, block, container, referenceBlock, uiComponent )
Look into your theme layouts for referenceContainer and, I guess, you'll find which definition si wrong.
Maybe you are using a custom/3rd-party theme that doesn't work with your Magento version?
