A tweet by tipster @L0vetodream strongly hints that an all-new iMac based on Apple's new ARM-based platform could arrive as early as March, adding the all-in-one to an increasing list of ARM-powered Mac devices.
https://www.notebookcheck.net/Apple-Silicon-powered-iMac-could-potentially-arrive-as-early-as-this-March-hints-tipster.513762.0.html