Uncaught (in promise) DOMException: CSSStyleSheet.insertRule: Not allowed to access cross-origin stylesheet

I’ve encountered this problem while attempting to inject CSS on a domain using Tampermonkey’s GM_addStyle() func, run-at set to document-start, as a result: some content on specific page/s does not load

Alternatively I set run-at to document-body but then, original theme would get displayed for a split second on every page refresh so I would like to avoid that approach

Any solutions? Thanks