QB Issue Resolution:

2 choices, more accurately track your on hand qty ( so the system knows you have enough to sell)  or
Sign in as sysadmin. cause the popup to appear, and click the check mark. “don’t show me this again” if you don’t see it you don’t have sufficient rights to dismiss warning boxes permanently.

Resolution for Issue 'In POS Desktop V18R10_01 getting a pop up in the Make a Sale screen titled Insufficient Quantity. How do I turn this off?' available: Yes (Solved).
Source: Intuit Community forum.

In POS Desktop V18R10_01 getting a pop up in the Make a Sale screen titled Insufficient Quantity. How do I turn this off?: this 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 issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Insufficient Quantity
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Error Recovery for Insufficient Quantity [Canada]
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