The safest way to get a portable version is to create it yourself using a legitimate copy of the game. This avoids the risks of malware often found on "free download" sites.
Chromebooks are more restricted than Windows PCs, but you still have options: stardew valley unblocked portable
A portable version of Stardew Valley is essentially a "no-install" setup. Instead of using a traditional installer that writes data to system folders (which is often blocked by administrators), you keep all the game files in a single directory. The safest way to get a portable version
The GOG.com version of Stardew Valley is DRM-free, meaning it doesn't require a launcher like Steam to run. stardew valley unblocked portable