As per the Esri doc:
It is a common misconception that only tools downstream of a model iterator will run multiple times. When a model contains an iterator, all processes in the model will be run multiple times.
All tools that need to run multiple times should be placed in one model with a model iterator and used as a submodel. The tools that only need to be run once should be placed in the main model, which calls the iterating submodel.
https://pro.arcgis.com/en/pro-app/latest/help/analysis/geoprocessing/modelbuilder/add-a-submodel-to-...
The workaround is to use nested submodels:
https://www.youtube.com/watch?v=yqYgs61w2YI