It is possible to not serve in the IDF, in apartheid Israel Jewish citizens have similar options to evade military service as in most other democratic countries. It just closes the door to lucrative army or tech jobs as having served in the IDF is prestigious and serving in the right units can be a major career boost. Hence, if you have served in the IDF, you have served in a genocidal occupation army and it is very likely that you have been at least complicit in committing war crimes.