The game is famously in a "perpetual beta" state. While the full version remains closed to a small circle of testers to avoid DMCA takedowns and maintain quality, a Public Demo was recently released.
This is likely what you are looking for if you want a "Mario Maker 3" experience on PC. It is a highly sophisticated fan game featuring over 500 themes and 22 different game styles. Mario Multiverse Game Download Beta
The most reliable source for the public demo is the official Mario Multiverse Discord server or the Mario Multiverse Archive on Itch.io . The game is famously in a "perpetual beta" state