Why in RouterOS v4.17 in Queue Tree no "comment" command? P.S. ROS v5.5 so non stable, than I will downgrade to v4.17.

Because queue trees don't have a comment property.

However, what you are trying wouldn't work anyway. There is no comment command in any RouterOS section. The syntax would be:

Do you plan to implement this feature (Queue Tree Comment Property) in the following OS version 4.xx?

Very useful property for peoples and scripts

I do not work for Mikrotik. You'd have to email support to get an answer to that question, or file a feature request.

However, typically new features are not added to old versions, and 5.x is the current branch.

what you are asking makes no sense. you can already add comments with the "set" command

what you are asking makes no sense. you can already add comments with the "set" command

it's exists in v5.x

ROS v4.xx not has this property

Simple answer to your question is that they're not going to backport new features into legacy versions.
If v5.5 doesn't work for you then run v5.0 or v5.4 as they've been mostly fine for me.

if a feature exists in v5.5, use v5.5