Making Neovim from GitHub the default file handler for text/source files

There may be a simple answer to this, but if there is, I'm not aware of it. I've downloaded the latest GitHub release of Neovim, because the one in the apt repositories is outdated by a few major versions. After following the installation instructions on the GitHub page, the nvim executable is placed in /opt/nvim-linux-x86_64/bin. From there, I can simply add it to my PATH in my .bashrc. This works fine for terminal use, but what if I got lazy and wanted to open files via the graphical file browser? It works fine with the apt version, because that is a deb package and everything. In the "Default Applications" app on Mint I've tried setting the default app for source code and text files as the nvim executable. It says it works, but when I try to double-click on a text file to open it, it doesn't. I've tried it numerous times, and I also tried adding the %U flag to it, to no avail. So as the title says, how can I set this version of nvim as my default app for text/source files?