Yes the activity for inactive customers (or vendors) will still be included in reports, etc.  It is part of your accounting history.  When you make them inactive, you just don’t see them on your lists anymore.  But they are still there & the history too.

Resolution for 'Are inactive issue: 'Are inactive customers sales still included in historic sales data?' available: Yes.

The Are inactive issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Are inactive issue yourself by looking for a resolution described in the article. If it is a complex Are inactive issue or you are unable to solve the issue, you may contact us by clicking here or by using other Are inactive support options.

For more information about resolving issues related to Are inactive in Quickbooks/QBO or to get support for the issue 'Are inactive customers sales still included in historic sales data?', click the link below: