If you have a spare monitor: display a virtual ‘co-worker’ on it by finding a Youtube streamer (search for pomodoro/ study with me/ gongbang)
Use a browser app. For instance a good Chrome/Brave App is Marinara Simple, configurable alarm sounds and/or opens a tab when timer is done (if you want)
Install a Desktop app: Pomotroid is available for all platforms https://github.com/Splode/pomotroid Nice and clean. Can be minimized to tray. Shortcuts are handy too
Use a phone app: For instance Focusmeter (Android) seems to work really well. Just installed it and I have seen no ads so far Forest App (Freemium ?) is quite popular, but I haven’t tried that one yet. Let’s you grow trees as a reward.