Learn Russian: Мы просто работаем и наслаждаемся процессом.

This is the key rule for this lesson! The Russian verb наслаждаться (to enjoy / to take pleasure in) governs the instrumental case, never the accusative. Many verbs expressing strong interest, enjoyment, or management require the instrumental. You can think of it literally as "delighting ourselves with the process."

Is наслаждаемся a regular reflexive verb?

Yes, it follows standard first-conjugation rules. The infinitive is наслаждаться. Because the subject is мы (we), you drop the infinitive ending, add the standard -ем ending, and finally attach the reflexive particle -ся.

In this sentence, does просто mean "simple" or "just"?

Here it acts as an adverb meaning "just" or "simply" ("we just work"). You will also often see просто used as a short-form neuter adjective meaning "simple" or "easy," as in это просто (it is simple).

Can abstract concepts like a "process" take the instrumental case?

Definitely! Once a verb like наслаждаться, интересоваться, or увлекаться demands the instrumental case, the noun must take that case regardless of whether it is a physical object, a person, or an abstract idea like процессом.