The noun involvement can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be involvement. However, in more specific contexts, the plural form can also be involvements e.g. in reference to various types of involvements or a collection of involvements.

Is interventions plural or singular?

The plural form of intervention; more than one (kind of) intervention.

What is the plural of intervention?

noun. in·​ter·​ven·​tion | \ ˌin-tər-ˈven(t)-shən \ plural interventions.