Thanks to @woxxom I've been able to get the embedded iframes to load by removing initiatorDomains:[runtimeId]
and instead using tabIds:[tabId]
and updating session rules instead of dynamic rules:
await browser.declarativeNetRequest.updateSessionRules({
removeRuleIds:[RULE.id],
addRules:[RULE],
})
On a sidenote, I found an unrelated error for my use case that says:
Uncaught SecurityError: Failed to read a named property 'document' from 'Window': Blocked a frame with origin "https://1xbet.whoscored.com" from accessing a cross m-origin frame.
This is the src
of the parent iframe embedded in the extension page. I'm not sure if this is something I should worry about.