I've gotten this error a couple of times when trying to install things recently.
First was the latest versio of node.
And just now, Acorn.
Guessing I'm on a too old version of Mint. I am certainly due an upgrade.
Yeah, this would suggest so: https://unix.stackexchange.com/questions/653465/how-to-install-glibc-2-28-on-linux-mint-19-3-cinnamon
libc is pretty much the fundamental library for nearly all your programs and libraries. It's very central, and Mint won't offer an easy way of updating to a newer version of it without a distro upgrade.
I'll just bite the bullet and upgrade then.
Yup, Upgrading Linux Mint 19.3 to Linux Mint 20 seem to have sorted. I can run Acorn now anyway.