It shouldn't matter much about the mixed i686 and pentium4 packages though going forward updating might fail.
Unluckily, there is no simple easy way to replace the packages, especially as currently RPM seems slightly broken where trying to replace a rpm seems to succeed but doesn't.
Basically have to get your list of packages,
rpm -qa --qf "%{NAME}\n" > packages.lst
unlock all the DLLs in \usr\lib, move /etc /usr /var out of the way.
Download
https://repos.arcanoae.com/anpm/pentium4/rpm-yum-base-os2-pentium4-2025-11-22.exe and run it in the root. Reboot.
And install all the packages in packages.lst.
Install the findutils and run
xargs yum --enablerepo=arca_inst --skip-broken -y install < packages.lst 2>&1 | tee packet.lst.log
The tricky part is the enablerepo arca_inst which is on the ISO, to quote Lewis, who posted most of this,
Mount the latest ArcaOS ISO, ensuring that the letter matches the path
rewriter setting (or change the path rewriter setting to match the
letter assigned for ISODrive).
Create local-rpm.repo, if necessary, or copy from backup
This is to catch things like arcamapper-ui which is only available on the ISO repostory.
Big job, good to have a backup before starting and I may have missed stuff like whether to enable netlabs.exp and not sure if the logging will work.
I might try this later.
As for your SeaMonkey problem, as I said, could not load xpcom errors are usually a missing prerequisite. Not sure what else might produce the error and since things are broken before the profile is loaded, I'm pretty out of ideas besides a broken DLL or similar.
Does the screensaver's Cairo Clock run? Just thought of fontconfig being broken and that would be an easy test.
memtest would also be good to run, I usually use a Linux ISO for memtest as they almost all have it, otherwise not sure where to get it and it runs on a bare system with no OS loaded.
Does your machine have any diagnostics, something else you could try.
