Buy European

All my fat kings drink RC

Afri Cola, Fritz Cola and Vitacola all three awesome and from Germany. Don't know if they're available outside Germany though, if you find any give em a shot.

Unironically, Lidl's “own brand” Freeway cola is p alright, I've never felt much for buying, and paying extra, for name brands.

Have you tried https://fritz-kola.com/en ?

Ok, I've got to promote Austrian lemonades from Murau, called Murelli, at that point - and their beer Murauer is really delicious btw

Not only has Murelli an alternative to Coca Cola, they also feature a really good orange lemonade (instead of Fanta) and if someone is a fan of 'Almdudler', their 'Alm-Rausch' is imho better than the original.

Here is the catalog of their offerings (although in German and I couldn't find a translation)
https://www.murauerbier.at/alkoholfreies/murelli-limonaden/

In france I've found carrefour cola to be an okay replacement, but would love to hear better options!