You can if you know what you’re doing, but you shouldn’t. In the context of this question holding back an Arch package is not a feature of Arch OP should rely on in every day use. In Debian this is supported (up to a point).

With Arch partial upgrades are explicitly not supported. You either upgrade all packages to the current version or you upgrade nothing. With Debian that’s different, you can upgrade a single package (with its dependencies) just fine. Technically you can do whatever you want of course.

That said, I wouldn’t really worry about upgrades, even on old hardware. Choosing a desktop environment is much more impactful if you worry about performance.