Foam is essentially core Obsidian inside VSCode/VSCodium, no access to plugins etc but there are VSCode plugins you can use as a replacement i.e. GitDocs can replace the Obsidian Git Sync plugin
If you search for comparisons most are pretty outdated now, for example Foam does have a graph view but Obsidian will still pull ahead in terms of features.
The main advantage for me is having everything in one program especially on my work PC where I can't install Obsidian but I am allowed VSCode.