Apply for furlough? You're not supposed to be able to apply for it. It's supposed to be determined by the employer based on the job role not being required (i.e. it's temporary compulsory redundancy), or based on the receipt of a shielding letter from the Government. If people are "applying for" it, it's being misused.
If there are a number of people doing the same job, and say only half of them were needed during the lockdown period, it's up to the employer to decide which half, and they could decide to ask people to apply.