How do I render a scene with a transparent background?

My scenes have always just rendered with a transparent background via V-Ray by default, but not anymore. Maybe I accidentally did something in the settings, but I don’t know. Now it just comes out with a random color as a background. How do I fix this?

Do you still save them as PNG files or have you changed and saved them as JPG? What kind of random color?

PNG

same render saved as JPG

Also, have you tried resetting?

Yes, I still save as PNG, and it’s literally any random plain color - green, grey, white. But I will try resetting, thank you, maybe that will help.