Pixel phones are also sold by some major stores in Finland such as Verkkokauppa.com and Gigantti. Some find it more comfortable to buy locally for warranty (and shipping) reasons. However, Amazon.de has usually better deals. There is also a Finnish price comparison site Hinta.fi where you can find some other retailers. I got my Pixel 6a from Amazon.de.
As far as I know the newer Pixel phones (6 and up) are now supported quite well by the major carriers (DNA, Elisa and Telia). I have used Elisa and Telia and they both have VoLTE and WiFi-calling, and it seems that DNA supports at least VoLTE. 5G is also supported by all three, though I have never used it. There might be some differences in support based on which plan you are on, and unfortunately, the carriers can be rather poor at communicating these differences.
The support did get a lot better during the last year so perhaps Google will extend their official support to Finland at some point.