@alphamachina I was able to fix this, eventually, but I'm not exactly positive which thing I did ultimately fixed it. So, I'll list them all:
Used DDU in Safe Mode to uninstall Nvidia driver, updated to latest Nvidia driver.
Extracted the offline Opera One installer, rebooted into Safe Mode, and installed from within Safe Mode using installer.exe within the extracted folder, but used All Users during the install process this time, instead of just my personal user account.
And success. The browser installed properly. This was after clearing all browser related folders, using CCleaner to remove the broken uninstaller link in Add Remove Programs, and then cleaning the registry of any Opera related entries (CCleaner does this as well):
C:\Users%USERNAME%\AppData\Roaming\Opera Software
C:\Users%USERNAME%\AppData\Local\Opera Software
C:\Users%USERNAME%\AppData\Local\Temp* (specifically any folders starting with 7z or Opera)
I think it was either installing from Safe Mode, installing to All Users, or updating my graphics driver from 577.00 to the latest driver from Nvidia. I also use two apps, FanControl and SignalRGB, and both of these hook into various drivers at relatively low levels, so it's possible those were interfering somehow. Installing in Safe Mode likely bypassed any possible interference.
One, or a combination of those likely ultimately led to it working, but as I said before, I also had some issues with my file system being a bit corrupted (everything else on my system worked fine, so it must have been a very limited amount of corruption).
To recap:
Initial Checks
Verified that your user account (jivef) had Administrator privileges.
Confirmed Windows Memory Integrity and LSA Protection were enabled, other antivirus scans disabled.
Checked the TEMP folder permissions and owner (your account).
.NET Framework and Redists
Inspected Visual C++ Redistributables (2010, 2012, 2013, 2015–2022) and repaired the latest versions.
Checked .NET Desktop Runtimes (6.0, 8.0, 9.0) and Windows Frameworks (3.5, 4.8).
Renamed .browser files in Framework folders (opera.browser → .bak) to allow regeneration.
Attempted ngen.exe update /force to rebuild assemblies; some errors were shown for WPF speller, but proceeded.
System Integrity and Repair
Ran:
sfc /scannow – found some issues, but not fully fixed.
DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /ScanHealth
DISM /Online /Cleanup-Image /RestoreHealth /Source:X:\Sources\sxs /LimitAccess (used Windows ISO as source due to component store corruption).
Enabled additional .NET features required for Opera installer to function, e.g., ASP.NET 4.8 and WCF HTTP Activation (after DISM fix).
GPU and Driver Troubleshooting
Suspected Nvidia driver issues (recent update via GeForce Experience).
Used DDU (Display Driver Uninstaller) in Safe Mode to completely remove GPU drivers.
Reinstalled known stable Nvidia driver (577.00 initially; later considered newer stable versions).
File System Checks
Ran chkdsk /f /r on C: to ensure the filesystem was healthy.
Verified SSD health via CrystalDiskInfo (reported 90% health).
Opera-specific Steps
Deleted/moved all Opera-related folders:
%LOCALAPPDATA%\Opera Software\
%APPDATA%\Opera Software\
Any leftover Temp installer folders (7z*) in %TEMP%.
Removed .bak from opera.browser files after repairs.
Downloaded offline full installer and tested running it from extracted folder.
Installed All Users option when prompted.
Event Viewer Observations
Found repeated c0000005 access violation errors in ntdll.dll during installer runs.
LiveKernelEvent 141 suggested GPU-driver or memory-related hook issues.
Observed BEX64 faults related to the installer module.
Result
After cleaning out all remnants, using a stable GPU driver, ensuring .NET features were fixed via DISM, and using the offline extracted installer, Opera finally installed successfully.
Settings and caches are stored in:
%APPDATA%\Opera Software
%LOCALAPPDATA%\Opera Software\
