I have always hated "m." domains for exactly this reason. They almost exclusively go one-way, mobile users get redirected to the mobile domain but desktop users never get redirected back, and all too often not only was the mobile version of the site objectively worse from the perspective of a desktop user but even the link to go back manually was either hard to find or nonexistent.

Wikipedia was one of the worst offenders, but lots of sites screwed this up in exactly the same way, and I feel it was a predecessor to modern "mobile first" web platforms that either treat desktop as second-class users or actively don't want desktop users.

[delayed]