Normally fertilization of tree plants outside in the open is stopped between mid-July to mid-August depending on the growing season length at the location to let the current year growth hardened before the frost. Does this also apply to potted fig plants that will be stored inside in cold storage after dormancy?

Can't say that I have been there, but if you want them to be dormant before storage, and you want them to be dormant at the same time as they would be, if they were left outdoors, I would assume that they should have a similar fertilizer regimen. If they could be stored non-dormant, and go dormant while stored, then it could be different.