i’ve seen someone made rollup j-pole on basis of fabric strip, with conductive fabric strips sewn on. so you could probably take an actual flag and do the same, because yagi elements need some thickness and flat strips are good enough. this looks a lot like yagi printed on pcb board, except that pcb board is stiff, and you’d need some rods to stretch the fabric. so there already is need to store long sticks. instead, you can make a regular yagi but with elements that can be detached when not in use. i bet somebody made 3d-printable clamps like that

there are commercial antennas available, but you will pay an arm and leg