Roving Cove Stair Railing Safety Net 10ft x 3ft, Baby Proofing Stairs Balcony Banister Rail Guard, Child Safety Stair Protection, Safe Rail, Almond Brown https://www.amazon.com/dp/B01AER7J3O/ref=cm_sw_r_cp_api_glt_i_S1YEGMCXXVYJN205KJSZ
We just got something like that. It wasn’t the prettiest option but it wasn’t terrible. Also the electronics still work like the tv remote and such.
The cats are likely way less worried about being out there than you are about them.
If it’s really a concern, weave some baby netting through the railing to prevent easy access.
I bought this kind of netting which works for my balcony: https://www.amazon.com/dp/B01AER7J3O/ref=cm_sw_em_r_mt_dp_U_xwCgFbA3M42J3
I would also just make sure theres no way for it to jump on something like a table/chair and then onto the top of the balcony railing