As far as I know about multitasking, not all threads have to be running simultaneously. Think about time-share property (or time-division multiplexing for cell phone people) as a parallel to multitasking on a single processor. IIRC, Intel's first true multitasking processor was the 80386, with hardware dedicated to multitasking, privileges, and virtual memory management, all of which are necessary to make an effective multitasking operating system. I don't know what MCU has that capability nowadays but multitasking is not just hardware but also sophisticated software that organizes tasks and relies on hardware to make each task feel like it is the only task running (virtual memory management for chaining up fragmented memory, memory/hard drive swap, and machine state save and recall etc.) and prevent unauthorized access to memory and other resources by tasks that don't have the privileges. Trying to do simple things all at the same time with multitasking is trying to kill mosquitoes with a canon. The OP may have programmed a general purpose computer for too long and he overlooked the fact that modern computers started not much more capable than arduino (8-bit, little memory) decades ago and back then people controlled multiple things just fine without multitasking software or hardware.
FYI, 80386 had a maximal memory of 4GB and virtual memory space of 64TB. I wonder if any lucky 386 has ever got close to that amount of memory.