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Hi B_Bogus,
First, my pleasure to assist you.
As per your description, please don’t worry, we can work together to narrow down and resolve the situation.
It seems you are unable to access SharePoint online frequent site pages. And Frequent Sites pages is always blank and it says "You don't have any recent activity. Start using SharePoint, May I know if my understanding is correct? if so, based on my test result, it seems I can access SharePoint online site page without any issue.
If you don’t mind (my humbly request, please don’t mind) could you please try to clean browser cache and try another browser or In-private browser to see if there is any other difference: Also please make sure you have a good network environment. And turn off the proxy or VPN temporarily.
To narrow down your issue, could you please confirm does this issue happened to a specific SharePoint online site page or all SharePoint online site pages as wee.
Also, could you please confirm, does other users in your organization have the same behavior as well or not.
Meanwhile, could you please let us know does you can't access specific pages related to Chart Web Parts within the SharePoint Online service.
Please don’t mind, this information is required to narrow down your issue to check whether this issue related with your organization Office 365 tenant level or not.
I appreciate your understanding and stay safe!!
Best regards
Waqas Muhammad