Can we give direct (dofollow) links to sub-domain & vice versa


I have a domain “abcd . com” and subdomain “blog . abcd . com”
my questions is that I will write article on subdomain and give an index (link) on home page or on other pages also on our main domain like normal article post.
So is it acceptable, can I give direct link?


If it is relevant to your content, yes.


Yes, there should be no issues as long as the linking is not spammy.