Jams still contain vitamin c, it is just reduced compared to fresh fruit

Jam is the classic way to preserve fruit.

It’s not ancient but blackcurrant syrup aka ribena was originally developed for this purpose when other fruit supplies were running low in Britain during the war

I didn’t think I could but interestingly enough discovered a technique that works earlier today. Basically get really close whilst staring at a point then gradually move away. It actually is an amazing effect