Does GOG Galaxy work well on an SSD? I notice some of my single-player games have slowdowns now.

Offline installers without galaxy work fabulously on an ssd and a bit slower on a hdd. No idea on galaxy as it’s a pointless waste of disk space.

I can't tell since I don't use Galaxy.
But I highly recommend a SSD. Samsung EVO series or Crucial MX500 are very solid and reliable.

Yeah, but I've never used Galaxy since 1.2?

Those slowdowns are probably other bottlenecks.

Galaxy works the same way as any other applications on an SSD in terms of launch speed. Steam on an HDD takes longer to load.

Your single player games shouldn't slow down just because Galaxy is or isn't on an SSD. Like the others said, you don't have to use Galaxy. Just install those games on your SSD and shortcut it from your desktop. If your games are slowing down outside of launching and loading screens, there are other reasons why including weak hardware (CPU, GPU, RAM, etc.), game settings too high, you need to update drivers and OS, power options, drives having < 25% free space, etc.

In short, yes, but that's because everything "works well" (loads faster) on an SSD. The slowdowns have nothing to do with your SSD, unless you find yourself in a weird "Windows messed up my controller drivers" type of situation, but I haven't heard of it being a thing since Windows 7 TBH.

No issues with Galaxy on an SSD, don't know how there could be frankly.

+1