Hi @Dr_Win_ST
you need to check the Project's permissions. Go to project settings > permissions. The permission you're looking for is "Delete issue".
It's likely, that currently it is set to project role "Administrators". You would have to add "Users".
Note: it's likely you are working with shared permission schemes. Any changes you do to the permissions in one project will affect any other project that shared the same permission scheme.
More on project permissions: Manage project permissions | Atlassian Support
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