downgrade from Catalina to Mojave

I just bought a refurbished MacBook Pro 16" from 2019. Unfortunately, though I didn't know or understand the drastic ramifications, it came with Catalina installed. After several difficult days of trying to get it to do the things I do, I have concluded I just need to go back and use Mojave so all my 32 bit stuff will work again. (Trust me, I really looked into 64 bit options for all the things I do and legacy hardware I have, and there are no realistic replacements available in 64.)

so i'm trying to create a boot disk and then wipe and install Mojave. But when I try to download Mojave, app store won't let me, says 'this version is not available.' And logging in from my old 2011 macbook, i get a bit further but then the app store says 'can't run this version on this machine'

how can i wipe Catalina and install Mojave? Do i need to return the new machine and buy one with Mojave loaded?