It takes serious engineering. And it's been done.The Dragon, from Zollner Elektronik AG.[1] About a third of the size of Gundam, mostly so it could be transported by road.
True quadruped. Best engineering in the giant robot space so far.
The Sultan's Elephant [2] was bigger, but less technically advanced. The headaches of transporting it were too much of a problem. Once your art project gets bigger than what can be moved by road or rail, there's a problem.
The Land Walker, from about 2006, was about a third of the size of the big Gundam. Biggest walking biped to date.[3]
There's also Eagle Prime, which is really a tracked vehicle.[4]
[1] https://youtu.be/qmbW5gvAX4U
[2] https://en.wikipedia.org/wiki/The_Sultan%27s_Elephant
[3] https://www.metatube.com/es/videos/9905/LAND-WALKER-Japanese...
[4] https://youtu.be/ePINYZK4p5Y