Hi Zeglash,
The error "Access to the resource is forbidden" you are getting is not related to permissions in SharePoint online or Excel. The error is very common and can occur while connecting SharePoint list to Excel or Power BI etc.
Please try the following method to clear permission in Excel and then check again:
1. In Excel, click Data>Get Data>Data Source Settings, click
Clear all permissions.

2. In Get Data tab, click
From Other sources>From Web.
3. In the Access web content box, select
Organizational account, choose the site collection under drop-down,
Sign in> Connect. When you try to connect your data source, it will allow you to re-enter your credential.

Regards,
Neha