Short answer
Yes. Aktar is free and open source under the MIT license. There is no subscription, no account and no upload limit on Aktar's side.
You only pay your storage provider for what you store and serve. For screenshots and everyday files that is usually a few cents a month, and some providers have generous free tiers. Cloudflare R2, for example, does not charge for egress, so popular links don't make your bill grow.
The source code is on GitHub, so you can read it, build it yourself or contribute. If Aktar saves you time, you can support development by buying me a coffee.