Though it can be done, I'm not a fan of creating flowcharts in Word, Excel, or PowerPoint. You can do it in all three, but I freely admit I'm biased toward Visio because it was designed more specifically for creating flowcharts and other diagram types.
Regarding Visio, I'd like to restate part of what Furkaan said above:
If you have a commercial, government, or education license for Microsoft 365, then it includes a free version of Visio called Visio for M365. (NOTE: Visio is NOT included with Home or Personal M365 accounts). The easiest way to determine whether you have access to Visio for M365 is to 1) log into you M365 account, then 2) in the address box in your browser, type visio.office.com
If you do have access to the free version of Visio, you'll see something like the screenshot below. Note that the Flowchart Template is top center and there's a Visio button on the left navigation toolbar:
A final note: if you're interested in doing more sophisticated things like creating swimlane diagrams or using data in your diagrams, you'll need an additional license for either Visio Plan 1 or Visio Plan 2.