redirection and permalinks not working in subdomain

I have several wordpress sites and have no problems with permalinks to webpages and posts. However having created a subdomain i am now encountering a problem where it will not redirect from /?p=12 to /title-of-post-content. I have tried two methods:
With a plugin – redirection and
Deleting the posts and starting again, but first of all setting the permalink to %postname%
However when i input the postname i get a “Server Error “404” message – page not found.”
I appreciate that this question may have been answered previously and if so could you please point me in the direction of the answer. The version of www.remarpro.com i am using is the latest version and i am using the THeme “Twenty Twenty-One”
Many Thanks you for your help
David

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