Between the S20 FE and Pixel 5:

• Price. The S20 has an introduction price of 650 (4g) or 750 (5g). The Pixel 5 is rumored to be around 650 (5g). Samsung prices tend to go down by some margins after physical release around the world. Pixel prices stay rather stable, but price drops are more common in the US, in Europe less so.
• Screen. S20 has a bigger screen at a higher max refresh rate. 6.5 to 6.0 inch, 120hz to 90hz.
• Modem. Pixel 5 has 5g, whereas the S20 comes in a 4g and 5g variant.
• Build. The S20 is a bigger phone. The Pixel is a more compact phone to hold. S20 uses a plastic body with Gorilla Glass 3. Pixel 5 uses an aluminum build with Gorilla Glass 6
• Protection. Both are rated IP68 rated
• Soc. The S20 has either the Exynos 990 (4g) or the Snapdragon 865 (5g). The Pixel 5 has the Snapdragon 765G. The difference will mainly be noticable in rendering tasks like gaming and productivity apps.
• Ram. The S20 comes with either 6 or 8 GB. The Pixel 5 with 8 GB.
• Camera. Both come with a wide and ultrawide, with the S20 having an additional telephoto lens. Processing is a subjective area, but detail wise the Pixel will have an edge, aswell as with color accuracy in terms of saturation.
• Software. Again subjective area. I quite like Samsung's OneUI, but I prefer stock Android. Both have 3 years of platform support.
• Battery. S20 has 4500mAh. The Pixel has 4080mAh. Battery life should be better on the Pixel since it uses are more power efficient Soc, has a smaller screen, and runs at a lower max frequenty.
• Extra. Both have optical fingerprint scanners. S20 on the side of the frame. Pixel on the back.

All in all they are rather closely matched, with the S20 having an edge in processing power and having an extra zoom lens and 3.5mm earphone port. The Pixel has a more premium build, cleaner software, more power efficient and has a better camera (imo.).

I personally care a lot about the camera and build quality, so I would get the Pixel. If you are more catered to having more processing power, and bigger better screen, and like the Samsung UI and camera processing, the S20 is a great fit.