You can buy and use a 3rd party screen protector, they just aren't very good, tend to bubble, don't fit well etc. So if you just want a temporary screen protector and can live with an annoying one in the meantime then just get one.
The flip phones all have the same issue of needing special screen protectors, fitted correctly, by Samsung. As the 3rd party ones just aren't very good yet, and don't seem to handle the folding well. So for now it's best to stick with Samsung proprietary protector until folding screens become more mainstream and better protectors become available