Do you agree with the concept of fwb’s?

Depends on the situation. I would want long-term commited relationship but if I don't have money to have kids, don't want kids, can't have long-term relationship due to job or lot of moving with less money, worried about not finding a partner in future due to age , etc ... In such situations, short-term relationships work but i wouldn't do short-term too just based on physical attraction. I would look for someone whom I really respect and like who will be ok with it .

If fwb means just sex without any genuine respect or friendship in it, i wouldn't be interested in it.

I think it's short-term relationships are useful for people who lack stability in life.