I tried many 98SE boot disks online, they all boot successfully on my mobile workstation from USB (C:\>), but all can't run the Windows 98SE Installer because of XMS Memory, giving an error like: This of course happens inside of himem.sys.
It's about how to get programs like the setup to run, not about the installation itself.
I don't know what's a healthy config.sys, is there anything that makes this computer's ram work with DOS like any computer, because Hyper-V doesn't fail himem.sys under 20+ GB of ram and I've read old computers having this issue with way lower amounts.
It's clearly about the bios not supporting big ram sizes, which already was a problem in 2003/2004 pc's, but no-one seems to have experience with this.
Edit: Nothing has worked yet as of 13 February, 2021.