The default value of a Boolean variable is False. As 10 mod 2 = 0 is True, robot will assign True to the isEven variable. However, the processing is paused before executing the activity with a breakpoint. So at the moment of the breakpoint, the value of isEven will still be False, and will be changed once Continue or Step Into button is pressed.
UiPath Documentation
Exam Topic: Examine and describe the activities and/or features used to troubleshoot, debug, and modify processes

NumberOfRetries property indicates how many times the activity will be executed overall. It is often misunderstood as 1 try + 3 retries (like in Orchestrator queues), however, it actually is simply 3 tries.
Even if Open Browser activity has ContinueOnError property set to True, it doesn't affect the Retry Scope, because Retry Scope activity has ContinueOnError set to False. So after 3 tries, if the required element still doesn't exist, the Retry Scope activity will throw an error.