Need Help developing a DAx measure for a complicated Gantt Chart

tj7933 , try a measure like

Measure =

var _max = coalesce(max(Calendar[Date]), today())
return
CALCULATE(
DISTINCTCOUNTNOBLANK('EMR_tblDeploy_DeploymentDetails (ALL)'[EmployeeID]),,
FILTER(
'EMR_tblDeploy_DeploymentDetails (ALL)',
'EMR_tblDeploy_DeploymentDetails (ALL)'[StartDate] >= _max && (
isblank('EMR_tblDeploy_DeploymentDetails (ALL)'[EndDate]) ||
'EMR_tblDeploy_DeploymentDetails (ALL)'[EndDate] >= _max )
&& ISBLANK('EMR_tblDeploy_DeploymentDetails (ALL)'[EndDate])
)
)

if the calendar is joined you need to use crossfilter refer

Power BI: HR Analytics - Employees as on Date : https://youtu.be/e6Y-l_JtCq4
https://community.powerbi.com/t5/Community-Blog/HR-Analytics-Active-Employee-Hire-and-Termination-trend/ba-p/882970

https://radacad.com/userelationship-or-role-playing-dimension-dealing-with-inactive-relationships-in-power-bi

Also check

Matrix as Project plan Visual: https://youtu.be/R25QoiyoSVs