Assalamu alaykum, is it allowed to give gifts to non muslim colleague for his marriage without attending the marriage ceremony?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no objection to gifting a non-Muslim.

'Umar ibn Al-Khattaab gifted his polytheist brother in Makkah a silk garment that was given to him ('Umar) by the Prophet .

The scholars concluded from this that it is permissible to keep ties with a non-Muslim by gifting him or giving him charity.

Tarh At-Tathreeb reads:

"This (narration) is proves the permissibility of keeping ties with non-Muslim relatives and being kind to them, and that it is permissible to gift a non-Muslim even if he is belligerent."

Allah knows best.