Please download the Windows Shell Extension from Krita’s download page and try to install it to solve your issue. Often it helps, but not always.
If you don’t use the current release version of Krita, you also can try if an update to the recent version 5.2.2 will fix it.
If those hints do not work, you have to grab far deeper into “the toolbox” to solve your issue.
You first have to uninstall Krita, and then you need to delete all remaining tracks from the Windows Registry.
If you should use an installation and update monitoring software, and used it to install Krita, this would be perfect, because these tools (in case they were worth the money) are able to remove all these tracks Krita’s installation left in the Registry for these file-associations, when you uninstall Krita with them. There are also such monitoring tools that claim to be able to uninstall and cleanup even installations they did not monitor, I’m not 100% sure but think that the uninstaller from iObit claims to do this too.
If you did not use such a monitoring software, you have to uninstall Krita the usual way via Windows → Settings → Apps (or Apps and Features), where you have to select Krita and choose to uninstall it,
or you can do it via Windows Start Menu → open the Krita folder → right click on Krita and choose Deinstallation.
Before you can reinstall Krita, you have to clean the Registry with one of the many tools that clean the registry and claim that they are able to remove the remaining tracks, ask your preferred search engine for registry cleaner to find such software.
And better search for test-results to the found software to compare them, some are pure rubbish (there is a reason why many of the tools do not have a very good reputation). Also be aware, the first hits shown by the most search engines are paid links, so only PR but not the best hit per se (even if they can be the best hit).
Or, if you are computer savvy, and you really know what you are doing, you can clean up the registry manually, but I guess if you would know how to do that, you never would have opened this topic.
In any case, if something is not clear to you, then please come back and ask before you do something that can’t be undone beside of re-installing Windows! The Windows Registry is not a toy, it is the most powerful and dangerous tool Windows has.
In case you store your files on OneDrive, this may be of help for you too:
Michelist