In my opinion, it's highly unlikely. Goku has mastered multiple forms and techniques that give him a wide range of powers. Saitama's one-punch style might not be effective against Goku's diverse skills and battle experience.
I don't think there's a clear winner. Both Manga Goku and Manga Saitama have unique and powerful abilities. It could come down to strategy, luck, or even the author's imagination!
Genos could be an unexpected opponent. He might be forced to fight Saitama due to some mind - control or a misunderstanding in the rules of the tournament. It would be really interesting to see how Saitama would handle fighting his own disciple, and how Genos would fare against his master's incredible strength.
Another theme could be the clash of different universes. Amazo is from the DC universe and Saitama is from One Punch Man. Fanfics might play around with how these two different universes' rules and powers interact when these two characters meet. Also, there could be themes related to respect and rivalry. Saitama is often very nonchalant about his power, while Amazo is a complex android with various abilities. How they view each other in the fanfic can create interesting storylines.
Saitama would win. He has shown incredible strength with just one punch. His power seems limitless, and in a fanfiction scenario, his simplicity and raw power would likely overpower Jiren's more complex abilities.
One possible plot twist could be that Jiren discovers a way to nullify Saitama's strength. Maybe he finds some sort of energy - draining technique that weakens Saitama over time. Another could be that Saitama holds back for some reason, like he wants to see the full extent of Jiren's power, and in doing so, he gets into a real struggle.
Perhaps there is a group of characters. There could be a mentor figure who has a high power level and helps the protagonist, who starts with a much lower power level. And there might be antagonists with their own distinct power levels that pose a threat to the main characters.
Well, it could have various unique features. Maybe it has a complex power system where characters have different power levels that drive the plot. For example, the power levels might determine the social hierarchy in the story world.
In Naruto fanfiction, power levels can vary greatly. Some fanfictions might boost the power of a character like Naruto himself, making his already strong Rasengan even more powerful, perhaps with new elements added. Others might focus on secondary characters and give them powers on par with the main characters. For example, a fanfiction could make Rock Lee able to use some form of ninjutsu on top of his taijutsu skills, which would significantly increase his power level in that fictional story.