What happens if you manually turn on the On-Screen Keyboard through settings->keyboard? Does it appear?
Also, I suggest that you run a System File Check (SFC) to check and fix corrupted system files. You can refer to this article (https://support.microsoft.com/en-us/help/929833/use-the-system-file-checker-tool-to-repair-missing-or-corrupted-system) on how to perform the SFC scan, and click on the blue link that says Windows 10.
I hope this answers your question.
--If the reply is helpful, please Upvote and Accept as answer--