Actually, much, but not all, of this may be possible. You can create a shortcut called, say, “Cycling”, use an action to set screen brightness to 100% (or whatever you want) and whatever you want to happen when you start your cycling workout. Then, go to the Automations tab on Shortcuts and create an automation to run that Cycling shortcut wherever you start a Cycling workout (which is one of the supported events in the Events section of Automations).
The one thing you may not be able to do is prevent your screen from locking. I don’t believe there’s any shortcut or action that will allow you to block that from occurring
thanks ?