https://en.wikipedia.org/wiki/Tanenbaum–Torvalds_debate
My take on that debate: They were both right, but they were optimizing for different things.
Tenenbaum was right in a theoretical sense and an eventual sense. Microkernels are better. Separation of concerns is better.
Torvalds was right in the early-mid 1990s and right in a pragmatic sense. More monolithic (or vertically integrated) kernels are easier to build and ship and are faster on smaller machines. A microkernel made little pragmatic sense on a early-mid 90s box. But keep in mind that these machines were far less powerful than a Raspberry Pi. My first Linux machine was a 66mhz 80586 clone with 32MB of RAM.
Once you have machines with dozens or even hundreds of cores, NUMA, and that host massively diverse multi-tenant work loads, microkernels start making a whole lot of sense. Once you have to containerize apps for security, they make sense too. They also make sense if we want to eliminate reboots, etc. They make much more pragmatic sense now than they did in the 90s.
Ultimately microkernels or microkernel-like systems will win.