Someone mentioned that the window size needs to be legal for it to count as a bedroom. What does that mean? Does anyone have experience with these rules?

Yes, there's a difference between regular windows and what they call "egress windows" for bedrooms.

You're right to check before proceeding. To qualify as a bedroom, especially in a basement, the room must have a window that meets certain escape and rescue requirements, commonly called an egress window. I went through this process while renovating my basement last spring. It’s not just about natural light or ventilation—it’s about emergency access. The window must be large enough for someone to exit through it and for a firefighter to enter. I highly recommend reading this resource on basement windows https://windowtechcanada.ca/requirements-for-size-of-egress-windows-in-basement-for-canadian-homeowners/ that breaks down the specific dimensions, opening mechanisms, and safety criteria. Following these guidelines saved me a lot of trouble during my permit approval.