Action Scheduler: found 39660 unexecuted actions; something may be wrong

The pending requests you’re seeing are likely due to a variety of reasons such as a plugin conflict, a server configuration issue, or a problem with the Action Scheduler itself.

Have you tried running a conflict test to identify any conflicting plugin? By switching to Storefront theme and see if the issue is gone, then if not, try deactivating all plugins and reactivating each to see which one causes the issue.?You can find a more detailed explanation on how to do a conflict test here.

Let us know how it goes!