Given arms and hands, a computer can do more varied physical work.
In this sentence, is the word 'given' participle or preposition? Please
explain it to me. Thank you so much.

"Given" here is a past participle. Not stated, but implied, are the words "IF IT WERE given arms and hands, a computer COULD do more varied [and] physical work."

This is the passive voice, which is formed by the verb TO BE in one of its various tenses plus the past participle of the verb in question (in this case GIVEN).