Sound like your Windows installation is damaged in some way.

You can mess with the DNS over HTTPs setting while Opera is closed. Open up the "C:\Users\yourusername\AppData\Roaming\Opera Software\Opera GX Stable\Local State" file with JSONedit in tree mode.

Under root, you can right-click on the dns_over_https node, choose "Delete selected node" and save your changes. That will make sure the setting is at its default (which is off). You can also try a test standalone installation of Opera if you can get the installer to not crash to make one.

I have a feeling that the DNS setting is not going to affect the crashing either way though, just maybe whether DNS works in Opera or not.

Another thing you can try for testing is to open up a command prompt while Opera is closed and run this command:

"%LocalAppData%\Programs\Opera GX\opera.exe" --disable-gpu --disable-extensions --no-experiments

That will basically start Opera GX is safe mode. Try that and report back if it still crashes.

It sounds like Windows is all messed up though where you need to wipe it out and reinstall it. But, other things you can check:

You can check and repair your system files.

You can use CrystalDiskInfo to check your drive's health.

You can run chkdsk to scan and repair your file system. See the "How to Run CHKDSK With the Right Flags" section if you're using an SSD.

Maybe there's something messed up in the Windows registry. A user at https://forums.opera.com/post/140034 used a certain registry cleaning program that helped. Can't vouch for it myself though, but if you use it, use just the "registry clean" option. CCleaner has some registry-cleaning tools in it. After you're done with them, you can uninstall them.

See https://www.softwareverify.com/blog/identifying-crashes-with-the-windows-event-log/ to see if you can find out the reason why Opera (or its installer) crashes. Might be revealing.

However, you can click "Edit" for DNS Server assignment", click the drop-down to switch to manual, turn "ip4" on and set your Preferred DNS to 8.8.8.8 and your alternative to 8.8.8.4. You can then save your changes and disconnect the connect and reconnect.

You can try 1.1.1.1 and 1.0.0.1 instead if you want.

In Opera, make sure "DNS over HTTPS" is off at the URL opera://settings/system.

I don't know how to do that

In Windows, goto "Settings -> Accounts -> Other users" and click "Add account".

In the Microsoft "How will this person sign in?" prompt, click "I don't have this person's sign-in information". Then, at the Microsoft Create account prompt, click "add a user without a Microsoft account".

Then, type testaccount for the username (don't set a password) and click next. That will create the account.

Then, click the start button, click your username, click "sign out" and then sign into the testaccount, give it a sec to set up things, launch Edge, goto https://www.opera.com/download, scroll down to the Opera GX section, expand it and click the link to the 64-bit offline package.

Once the installer is downloaded, launch it, click "options", make sure "install for" is set to "current user", make sure "install path" is set to "C:\Users\testaccount\AppData\Local\Programs\Opera GX", uncheck all the option boxes and install.

Does Opera install then?

If so, you at least know that it's just something messed up with your main account.

You can then sign out of the test account, sign back in to your main account, go back to "Settings -> Accounts -> Other users" and remove that test account.

You can temporarily create a new user account on Windows (a local one not tied to a Microsoft account) and see if the installer works fine there. The problem might be limited to your user account.

In "C:\Users\yourusername\AppData\Local\temp\.opera", you should see installation logs. Look in "C:\Windows\temp\.opera" too if you were trying to install for all users instead of the current user. In the log for the latest install attempt, you might be able to find the cause. Just note that there are always some errors in the log, so posting the full log (with each line indented by 4 spaces, which is easy to do with Notepad++ with ctrl + a and then tab when indenting is set to 4 spaces in settings -> Preferences -> indentation) here might be necessary so everyone can look at it.