I am having the exact same issue, just started yesterday.
The block editor recently started having another problem, too, where it can’t accept numbered bullet points. Loads of troubleshooting and many hours later, I discovered that tiny detail was preventing my drafts from saving or publishing…
To take above recommendations for this issue, I just opened the editor in a new browser and cleared cache, but the issue persists. (And if you don’t have any custom code blocks, that wouldn’t be an issue for your site either). Not sure when these issues will be resolved.