[ETC] Looking for suggestion for a one-off!

I am a player in a weekly DnD 5e group online. I would like to have a one off module that is ready in case my DM wants to take a break and we still want to meet. (I don't want him to always feel obligated to be ready or rush a story)

I think my best option is Roll20.

I would like for the setting to include premade characters and the platform to be user friendly. It must be an online platform.

I have been a DM before for a one-off. I am not the best DM but it is not about being great; It is about having fun and our DM feeling like they can take a break to avoid burnout.

any suggestions?