Most switches stall on a false premise: that one app must do everything Photoshop does. Nothing here is that app, and chasing it wastes weeks. The faster route is to pick by which half of Photoshop you actually use. For photo retouching, compositing, and general raster editing, GIMP is the most complete option, with Pixelitor a lighter alternative built around layers, masks, and more than 110 built-in filters. For drawing and illustration, Krita and MyPaint are purpose-built painting apps. For quick everyday edits, Pinta and Drawing keep things simple, and for game sprites, PixiEditor handles pixel art, vectors, and animation. And for enlarging low-resolution photos, Upscayl, RealScaler, and QualityScaler do AI upscaling entirely on your own machine, a different job from pixel editing.
Set expectations on file fidelity before you move anything. Opening a PSD is not the same as preserving it: raster layers, basic masks, transparency, and many blend modes usually survive, while text layers, adjustment layers, smart objects, and proprietary filters rely on Photoshop behavior and often do not. Keep the original PSD untouched and migrate a copy, comparing it against a flattened reference export. Two known gaps are worth checking up front, CMYK and print color, where GIMP is RGB-centric, and pen tablets, where you should test pressure and shortcuts on real hardware rather than trusting screenshots.
Fit RAW photos into the workflow deliberately, because most of these editors are strongest after RAW development, not as the first stop. The common path is to process RAW files in a dedicated converter, export a high-bit-depth TIFF, and then retouch or composite from there, keeping the original RAW files untouched so you can reprocess later. The payoff across all of this is that your finished work lands in open formats like TIFF, PNG, and PDF that any tool can reopen, on software that keeps running whether or not a subscription cleared this month.