Upscayl is a free and open source desktop application that lets you upscale your low resolution images using advanced AI Models. Upscayl is a Linux-First Application that prioritizes Linux builds but is also cross-platform.
Disclaimer: I do not own this application or tool. I'm just here to share it, but you're free to support the developer. The tool/application's working capability and other issues depend on keeping the project alive by the author. Use it at your own risk.