When Spyro Reignited Trilogy was announced, Activision specified that PlayStation 4 and Xbox One were the only platforms the game was coming out on at launch. However, the website for the game in certain regions seems to be implying that might change quicker than we think.
On different regions for the Spyro Reignited Trilogy website, such as the UK, scrolling down to the preorder drop-down lists for the game lists PC and Switch as available preorder platforms in addition to the known PlayStation 4 and Xbox One versions.
Considering that it is only appearing for certain regions, and the fact that Switch is listed twice, probably means this is some kind of mistake. Maybe code was taken from the website for the Crash Bandicoot N. Sane Trilogy, which is available on all the aforementioned platforms, and was not as well-excised as they thought. Or Switch and PC versions could be pending announcements that simply went live way too early.
We have reached out to Activision for comment but did not receive any response by the time of writing.
Spyro Reignited Trilogy is releasing on at least PlayStation 4 and Xbox One on September 21.
My feeling is that this is probably a glitch, but I do expect the trilogy to come to those platforms eventually. Maybe Activision is waiting to see how Crash does first.