Can I use remarketing campaigns as a standalone campaign?
It is recommended to have a full-funnel approach to your campaigns. Therefore, instead of having a standalone retargeting campaign, have a top-of-the-funnel campaign - mostly lookalikes if you are unsure about the targeting. (The ad platforms are slowly transitioning towards not having audience targeting controls for the marketers. ASC, and PMax, are all a sign for it.) Now, these audiences from the top of the funnel campaign are pushed towards the middle of the funnel, and your retargeting campaigns kick in pushing them further.