Does doubting one's attentiveness while reciting adhkar or being forgetful during their recitation necessitate repeating them? And is this considered waswas (whispers from Shaytan)?

The doubt that the questioner experiences, along with the repetition and re-recitation of adhkar (remembrances), is a form of waswas (whisperings/obsessive thoughts) that he should avoid. We advise him to suffice with reciting the Qur'an, supplications (du'as), and adhkar without repetition. For whoever recites the Qur'an or remembers Allah gains the reward of recitation and remembrance, even if he is not fully attentive, because warding off harms takes precedence over gaining benefits.