Ok so for a transformer like this https://www.we-online.com/catalog/datasheet/7491182012.pdf

the current saturation is 0.8A but it is rated at only 0.35A on the output for 12 v.

My question is if I am trying to use the transformer(in a flyback topology with TNY290) to generate only 5V does that mean I am able to get more current through the transformer? I know the wire thickness is what is limiting the current but my logic is that the power capability would be 4.2W so I could use 5v and 0.84A.

I just want someone to explain why I am wrong.

thanks

ps the reason I am wanting to use a transformer with a higher rated voltage is that I want a turns ratio that is closer to 10:1 instead of 20:1