If the film festival allows you to use this kind of tools, then yes, you can use Wondershare Filmora to create content. However, based on my knowledge, I know you must follow some rules, even for these film festivals, so it's best to get in touch with the judges or administrators to ask about the specifications required for movies entered or submitted.
If you indeed submit a movie this way, make sure to avoid using anything that is related to Filmora (intro, end credits, effects, etc).