Thanks, i understand now. Makes sense. Might have to use someone else's computer to purchase... all good thnxx
You're welcome. Note another computer won't work if Pages, Numbers and Keynote are currently installed.
You can just create a new partition on your computer. Then install a newer macOS version. This only needs to be temporary. Even if it's an older iMac. You should be able to use the Dosdude1 Catalina Patcher to get to Catalina.
Once everything is associated with your Apple ID. You can restart into Mojave and verify you can install the various iWork apps. Then delete the Catalina or newer partition.
You could also do this to an external HDD/SSD.
In any of these instances you need to create a USB installer to boot off of and manually install a newer macOS to your selected partition or disk.
I think a clean install would include Numbers. Like I said, it has been pre-installed on all my Macs for years now. IMO, the only reason it wouldn't be there is if somebody actually deleted it.
Perhaps an extreme solution, but you could re-install Mojave as described here and it should be included
Download and install current or previous versions of the Mac operating system on compatible Mac computers.
support.apple.com
A clean install is macOS only and various base programs integrated with the OS, Utilities and some basics like Textedit and Preview. Numbers, Pages, Garageband, &c are not part of the installer and can only be downloaded from the App Store after a clean install or restored from a backup.
The issue is that the App Store makes you purchase free apps not associated with an Apple ID. Even ones which come with Macs. From what I can find, will only let you purchase if your Mac supports the current version. It's just one of those App Store oddities. Until the app is associated with your ID. You can't download the older version.