My bedroom window keeps fogging up between the panes. Is that fixable or do I need to replace the whole thing? It's really annoying

That means the seal is broken. Once that happens you can't really fix it properly. You'll probably need a new window unfortunatel

Yeah the seal's gone and moisture gets trapped inside. Had the same thing happen in two of my rooms last year. Ended up replacing them because wiping the outside doesn't help when it's between the glass. I got mine through WindowTech https://windowtechcanada.ca/ and they explained the seal issue to me. New windows fixed it completely. It's not cheap but leaving it just makes the problem worse over time and looks bad too