Fallout 3 and New Vegas both have massive issues. You may be better off using Lutris with the GOG version on the Steam Deck and finding a config that installs the performance fix mods.
It checks out given the articles coverage of just how poor the memory latency is once you exceed the tiny 4MB cache.
There are ways to “fix” it but they tend to suck. You can crank the draw distance of objects to the minimum but if it’s not done dynamically then every other scene becomes terribly ugly/broken. You can also install mods that remove some of the clutter but how do you know which clutter to remove? Some of it is aesthetically important and the tone of the scene can change dramatically by randomly removing stuff.