>Chrome apparently has a flag

And even then the options were confusing: 'Enabled' and 'Enabled available in settings'

I first tried with Enabled, didn't work. Then tried the settings option, which showed reader mode option under 'Appearance'. After turning on this setting, the icon shows up.

I know this has been an on and off thing with Chrome, but, yes, it does appear to be back and works now.

works now in brave, the setting is extremely confusing, you have to set it to "enabled and available in settings"