Turns out you actually can get a minifig to fit in the newest technic excavator (set 42121) by simply removing the red seat. : r/lego
LEGO MOC Red Excavator by jb70 | Rebrickable - Build with LEGO
Amazon.com: FULHOLPE Technology Excavator Bulldozer Building Set, 2.4G/APP RC Front Shovel Rope Excavator with Motor, Excavator Building Block Compatible with Major Brands - 2968 Pieces : Toys & Games
LEGO MOC Poclain HC300 by Levihathan | Rebrickable - Build with LEGO