Century Gothic Greek glyphs

The Century Gothic available from Adobe Fonts is actually Century Gothic Pro in OpenType CFF format licensed directly from Monotype. It does not support the Greek character set. Per Monotype, it does claim support for Western Europe, Central/Eastern Europe, Baltic, Turkish, and Romanian languages with 418 glyphs in total.

The version of Century Gothic bundled with Office is a special version of Century Gothic in TrueType format that was designed to match the “advance widths” of ITC Avant Garde, one of the base 35 fonts that were available with Adobe PostScript printers going back 35 years. That special version of Century Gothic has a total of 666 glyphs adding support for Greek and other symbols and alphabetic glyphs requested by Microsoft. See https://docs.microsoft.com/en-us/typography/font-list/century-gothic for more information.

If you need a version of Century Gothic that has Greek support and that can be licensed for web use, you need to license Century Gothic WGL from Monotype. It has that 666 glyph complement and can be licensed for web use. You may license it directly via https://www.fonts.com/font/monotype/century-gothic-wgl specifying either desktop and/or web use for licensing. Note that a web license is not inexpensive!