Hi there, @Glang.
Inactivating your customer or vendors does lower your active list count. I'd be glad to provide more details about this and guide you how.
When you choose to inactivate customers and vendors, this lowers your list count. However, this doesn't lower your overall list count. Your inactive customers and vendors are still included in the counting of customers and vendors.
You can follow the steps below in inactivating a customer:
Then, you can follow these steps to inactivate a vendor:
As for condensing your data, this is currently unavailable in QuickBooks Online. However, this is available in QuickBooks Desktop.
You can also visit our Help Articles page if you want to learn more "How do I" steps.
Don't hesitate to let me know if you have any other questions. I'll be here to help you.