Sikhism

Sikhism is an Indian monotheistic religion. This is the Mool Mantar, the fundamental creed of Sikhism:
ੴ ਸਤਿ ਨਾਮੁ ਕਰਤਾ ਪੁਰਖੁ ਨਿਰਭਉ ਨਿਰਵੈਰੁ ਅਕਾਲ ਮੂਰਤਿ ਅਜੂਨੀ ਸੈਭੰ ਗੁਰ ਪ੍ਰਸਾਦਿ

ੴ	Ik onkar	There is only one God
ਸਤਿ ਨਾਮੁ	Sat Nam	Eternal truth is his name
ਕਰਤਾ ਪੁਰਖੁ	Kurtah Purakh	He is the creator
ਨਿਰਭਉ	Nir Bhau	Without fear
ਨਿਰਵੈਰੁ	Nir Vair	Without hate
ਅਕਾਲ ਮੂਰਤਿ	Akaal Moorat	Timeless without form
ਅਜੂਨੀ	Ajooni	Beyond birth and death
ਸੈਭੰ	Saibhang	Self-existent
ਗੁਰ ਪ੍ਰਸਾਦਿ	Gurprasaad	By the Guru's grace

Since there is only one God, how can there be so many monotheistic religions like Judaism, Christianity, Islam and Sikhism? Is the God in these religions the same God?

Let us look at how God introduced Himself to Moses personally while Moses was at mount Sinai:

The LORD came down in a cloud, stood with him there, and proclaimed his name, "the LORD." The LORD passed in front of him and proclaimed:
The LORD - the LORD is a compassionate and gracious God, slow to anger and abounding in faithful love and truth, maintaining faithful love to a thousand generations, forgiving iniquity, rebellion, and sin. But he will not leave the guilty unpunished, bringing the consequences of the fathers' iniquity on the children and grandchildren to the third and fourth generation. (Exodus 34:5-7 CSB)