Regarding application of ring signatures The wikipedia page of Ring Signature states:

Another application, also described in the original paper, is for
deniable signatures. Here the sender and the recipient of a message
form a group for the ring signature, then the signature is valid to
the recipient, but anyone else will be unsure whether the recipient or
the sender was the actual signer. Thus, such a signature is
convincing, but cannot be transferred beyond its intended recipient.

Can someone please explain the practical application of this concept? I can not make any sense of it? In what scenario it could be useful?
To understand the application, it is useful to contrast this with the use of regular signatures.
Imagine Alice sends a message $m$ to Bob together with a signature $\sigma$ of $m$ under her own public key $\mathsf{pk}_A$. A regular signature scheme now has two important properties:

It's publicly verifiable, i.e., anyone can verify that the $\sigma$ is a valid signature of $m$ under $\mathsf{pk}_A$.
It's unforgeable, i.e., only someone in possession of the corresponding signing key $\mathsf{sk}_A$ could have produced a valid $\sigma$.

The combination of the two, together with the assumption that Alice has a strong incentive to keep her signing key secret¹, leads to a property called non-repudiation. This means that the recipient can prove to a third party that the Alice really did send $m$ simply by producing $(m,\sigma)$.
Now, say $m$ is something legally or morally incriminating. Then, among other things, this opens Alice up to blackmail. Bob can threaten to release $(m,\sigma)$ which would prove to the public or some third party that Alice said $m$.
Alice understandably would like to prevent that. So this is where ring signatures come in. If we replace the signature scheme above with a ring signature scheme, then Alice would be sending $m$ together with a ring signature $\sigma$ of $m$ under the set² of her own public key and Bob's public key $\{\mathsf{pk}_A,\mathsf{pk}_B\}$.
A ring signature is still publicly verifiable, however the unforgeability now only guarantees that the signer must have known one of $\mathsf{pk}_A$ or $\mathsf{pk}_B$. This means that Bob can no longer prove to a third party that Alice sent $m$, since Bob himself could have simply computed $\sigma$ himself.
He can of course still try to blackmail Alice, but he can no longer rely on the security of the signature scheme to do so.

¹ This is where this argument could break down in practice.
² Sometimes also called ring, even though the name ring signature actually comes from the way the first such scheme computed it's signatures.