obj to 3mf conversion is doable in the sense it is possible to use 3D OBJ files for making new 3MF files, typically for the purpose of 3D printing. Many tools nowadays adopted 3MF format, so it shouldn't be hard to find one that will suit your needs.
Many guides and howto's can be found on the Internet about 3MF format, even some YouTube videos covers the topic of making new 3MF files.
Updated: August 16, 2023