You can likely watch a video and work out with no biofeedback. You will have to give it a try to see if it will let you do so.
This is Apple's answer to the general question;
Do I need an Apple Watch?
Yes. Apple Watch personalizes your Apple Fitness+ experience by integrating your personal metrics, like your heart rate and the calories you burn, into every workout. It brings them to life on the screen to keep you informed and motivated. To use Apple Fitness+ on your iPhone, iPad, or Apple TV, an Apple Watch Series 3 or later is required.
M1 Mac mini, macOS 12.1; Watch, series 5 GPS/cellular, watchOS 8.3; iPad Pro 2nd Gen, iPadOS 15.2; iPad Air 2, iPadOS 15.2; iPhone 12 Pro, iOS 15.2; TV 4th Gen, tvOS 15.2; HomePods, audioOS 15.2 and Airport Express w/ Airplay 2