Windows has several separate reasons to stop what you're doing: the display turns off, the PC sleeps, the screensaver starts, and the lock screen appears. They're controlled by different settings, which is why fixing one often leaves another still biting you.
1. Change the power plan
Open Settings → System → Power & battery and set Screen and sleep to Never while plugged in. This is the cleanest option when you control the machine, and it needs no extra software. The catch is that it's all-or-nothing: you have to remember to put it back, and it does nothing for web apps that decide you're away on their own.
2. Use a system-level keep-awake utility
Tools such as Microsoft PowerToys' Awake tell Windows that something is still in progress, so it holds off sleep and screen-off for as long as you ask. They don't touch your saved power plan, which makes them easy to turn on and off. They act on the whole computer, whichever programs are running.
3. Use a browser extension
A Chrome extension such as Windows Mouse Mover works inside the browser. It asks Chrome to hold a screen wake lock, so the display stays on, and it simulates small amounts of page activity so web apps that judge idleness from the page keep seeing you as present. It only runs while Chrome is open, and it doesn't change Windows power settings.
Which to pick
- Own the PC and only need the screen on? Change the power plan.
- Running a desktop task and want sleep blocked temporarily? A system-level utility.
- Working in web apps such as Slack, Teams or Gmail in the browser? An extension fits.
None of these will override a policy set by your organization. If a lock timeout is enforced by IT, treat it as a rule rather than a setting to work around.