Thank you for your question.
Mark 3:29 But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation:
The Holy Spirit is the power of God by which Jesus did his acts of healing. Casting out ‘devils’ (Greek daimonion) called ‘unclean spirits’ was the curing of mental illness. The scribes refused to allow that it was the power of God. They told the people that it was the power of an Idol.
22 And the scribes which came down from Jerusalem said, He hath Beelzebub, and by the prince of the devils casteth he out devils.
Beelzebub was originally a Philistine deity worshipped at Ekron. The Jews hadn’t believed in Idols since their return from the Babylonian captivity.
The miracles were God’s witness of the veracity of Christ’s message about the gospel of the kingdom of God.
Luke 11:20 But if I with the finger of God cast out devils, no doubt the kingdom of God is come upon you.
By asserting that the power doing the healing was the unclean spirit of an idol which had no real existence, the scribes were blaspheming the Holy Spirit.
30 Because they said, He hath an unclean spirit.
It was an accusation without foundation which they used to try to stop people listening to Jesus.
John 10:20 And many of them said, He hath a devil, and is mad; why hear ye him?
As a body, they did not believe it themselves as Nicodemas says.
John 3:2 The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him.
They treated the power of God with contempt and lied to the people and so blasphemed.
We in our day are not in danger of committing this offence because we do not witness the power of the Holy Spirit in action.
I hope this helps.