Problems recovering High Sierra onto an old MBP

I am trying to rejuvenate an old MBP for a friend. Since it wasn't booting, I erased the "OS X Base System" internal volume and rebooted into recovery mode. In case it is relevant, I formatted it as "Mac OS Extended (Journaled)" as it was previously Mac OS Extended. So far so good.

Unfortunately, when I ask it to reinstall High Sierra (the default option), I repeatedly get the message that the recovery server could not be contacted.

I have tried checking the date, and while I don't get a regular terminal login but a Bash 3.2 terminal with root (#) privileges, it appears to be correct. The only possible error is that it is reporting a time in UTC while here in the UK we are now on BST (DST -> UTC +1). I can't see how to tell the date command that, as I can't work out what the "-d dst" option does and in any case I'm not even sure if it is relevant.

I have tried using my 2019 MBP running Sonoma 14.4.1 (not quite up to date yet) to download an installer so that I can create a bootable USB, but App Store tells me that either it is not available or else my MBP is not compatible with it (which I can believe).

So nothing is working, and I am extremely reluctant to go to a non-Apple site promising me a download of the disk image. Where do I go next?

Thanks