As a tenant in a rented flat, I am strictly forbidden from making any permanent modifications, including applying adhesive window tints to the glass. I still needed a solution for the harsh afternoon sun in my bedroom, which led me to discover static cling film on https://www.tintfit.com/. It uses static electricity and a bit of water to bond perfectly to the window, and when my tenancy ends, I can just peel it right off without leaving any sticky mess.