I'm having a similar issue with Big Sur on an iMac (4 GHz Quad-Core Intel Core i7). I have the latest Opera version (72.0.3815.378). If I leave a tab for a second or two (e.g., when I open a new tab), it is blank when I return. If I wait for a while it will usually repopulate, but it can take 15 seconds or longer.

The latest update 73.0.3856.257 seems to have fixed the issues I was experiencing. Tabs are not blank when I switch between them and tabs keep streaming, even when I move away from a streaming tab to another tab.

One thing I do notice, however, even with the update, is that some tabs that are streaming content stop streaming the content once I leave the tab for another tab. That wasn't the case before. For example, in the past I could listen to what was happening in a streaming forum tab while I looked at other tabs. Now, the second I leave the streaming forum tab, the forum stops streaming. I really need the tabs to keep streaming. (It does keep streaming Youtube tabs, even when I leave them, so I don't know what the difference is between the streaming forum tab and a streaming Youtube tab.) It does let me go to another application, however, and it will keep streaming, so it is just the tab switch that causes the issue.

The developer version (74.0.3890.0) does appear to address the blank bookmark issue on my iMac (4 GHz Quad-Core Intel Core i7) | Big Sur 11.01 machine. Thanks for the heads up @nintendork07.

I updated to 72.0.3815.400 today, but the blank tab issue remains. I leave a tab and but when returning to the tab it is blank for 15 seconds or so. I never had the issue with prior versions of Opera, but that was before updating to Big Sur 11.01.

I'm having a similar issue with Big Sur on an iMac (4 GHz Quad-Core Intel Core i7). I have the latest Opera version (72.0.3815.378). If I leave a tab for a second or two (e.g., when I open a new tab), it is blank when I return. If I wait for a while it will usually repopulate, but it can take 15 seconds or longer.