Basically just do the normal e sync, maybe e build then cd out/Release or whatever is your build directory and do ninja -t compdb > ../../compile_commands.json. Now you have compile_commands.json in root of Chromium, for me, nvim and Zed automatically picked it up. You can also move or symlink the file to ./electron/, where the Electron source code is, if you want to open it, instead of the whole Chromium source, as a project.
Source: https://www.chromium.org/chromium-os/developer-library/guides/ides/chroot-clangd-guide/