Well, that is the way Microsoft rolls. They require the current release of macOS and the two previous major releases in order to install Microsoft 365 or either Office 2019/2021 for Mac. You have worthless software until you have a Mac that can upgrade to macOS Catalina or later. There is no workaround with macOS 10.13.
That 2017 MacBook Air is supported by macOS Monterey via upgrade from the Mac App Store. You can also install Catalina, or Big Sur via the How to get old versions of macOS site, and the respective link to the full installer in the Mac App Store. Use Safari only for that link, and always perform a last Time Machine backup prior to any operating system upgrade.
Also, understand that Catalina and later strictly support only 64-bit applications, printers, and scanner drivers. Use the free Go64 application to get a list of your existing 32-bit applications, and if third-party vendors offer 64-bit versions of those applications. Check the specific printer/scanner vendor sites for driver updates in 2021, the later the better.