Starting Summer’21, it is now possible to make use of ISCHANGED, ISNEW, and PRIORVALUE functions in record-triggered flow formulas.
The biggest advantage I see is getting rid of a few dependencies we might have between flows and process builders. This addition will certainly assist in moving away from extra process builders/workflows, built explicitly to take benefit of these functions.
Also, when moving or copying formulas containing, ISCHANGED and PRIORVALUE into record-triggered flows, use the $Record global variable.
Workflow: ISCHANGED(Account.AccountSource) Flow: ISCHANGED($Record.AccountSource)
The ISNEW function requires no changes because it has no parameters.