After reading the below thread , we find out that the binaries referenced requires ArcGIS Server 10 or ArcGIS Image Server 9.31 , in our case , we have ArcGIS Pro 2.8 , ArcGIS Enterprise 10.8.1 , ArcGIS Enterprise 10.9 . the ECW.zip Plugin referred to in the below thread is not compatible with the above mentioned releases , the question is from where shall we download those files that are compatible with the above releases! , does ESRI have them or shall we contact Hexagon to have them? , in the other hand , what are the steps required to be done to enable the ArcGIS server 10.8 , 10.9 able to publish ECW image services , do we need only the place the above binaries under the ArcGIS Server installation bin directory or do we have to do other steps!
For working with ArcGIS Enterprise 10.8.1, you need ECW for ArcGIS Server Plugin 2020 for Windows Update 2 . Please check the link for more details. In case of any further query on it licensing, please contact Hexagon Geospatial.
Hope it helps.