Thanks for your reply. Please, can you further explain why you wouldn't use Next.js or Firebase for building a product as a solopreneur? Maybe because I don't have much experience with Rails but I'm still failing to understand how it's much better in your opinion.
Also, I think Digital Ocean doesn't have a free tier. That's my other point: I can't find a reliable, fast way to try out new ideas spending literally $0 using something like Rails. That's pretty easy to do using JAMStack, though.