Negative cost but also negative revenue / productivity loss if not done properly.
Most data appears to show the hybrid model is the best for productivity. WFH several days a week, enabling focus and limiting distractions. Work from the office a couple days a week to enable coordination, connection, innovation, and alignment.
This forced experiment in 100% WFH was clearly bad for productivity. The reason tech companies provided so many perks in the past wasn't simply as a recruitment technique. A lot of it was to create an environment where workers worked longer hours and thus the firm got more productivity out of each worker. The cost-benefit analysis clearly supported that before. A caterer's salary is far lower than an engineer's.