You could try looking in the Purchased section of the App Store to see if it would let you download an older, more compatible version of Numbers. Might work, might not.
With respect to Microsoft, it's their policy not to support anything other than the most recent three major versions of macOS. I've seen reports in these forums that they have even turned off DRM activation servers for some older versions of Office … so it's possible that if you find your Office CDs/DVDs, reinstall, and enter the codes that came with those discs, Office still won't work.
Once upon a time (less than a year ago), LibreOffice ran on High Sierra. Now the current versions require Catalina. The LibreOffice site does have an archive of builds of old, unsupported versions, and I'm sure there are some that run on High Sierra there. The trouble may be identifying them - the site seems poorly organized wrt to answering the question "what is the latest version that will run on macOS _______?"
IIRC, LibreOffice 7.4.7 ran on High Sierra when it first came out, but then got re-released (?) with a requirement for Mojave. So you could start around there and go backwards to slightly lower versions.
https://www.libreoffice.org/
https://downloadarchive.documentfoundation.org/libreoffice/old/
Since you. have an Intel-based Mac, you would want an "x86_64" build. I'm pretty sure that "aarch64" would be a nickname for Apple Silicon.