why doesn't this loop.

Following youtube video on EQ and it would be useful, as in the video to just loop a part of the clip with sound as otherwise it goes to clip with no sound, then I have to close the EQ window and back up.

So I do what he does, set the loop, click the + and drag around an area, but it doesn't loop, it goes past.

Loop Enable: Command + Forward Slash
Loop Selection: Option + Forward Slash

Refer to the Resolve 18 Manual:
Page 3479 | Chapter 168 | Transport Controls, Timeline Navigation, and Markers

Resolve 17 Manual > Page 3181

Reading through the manual sequentially, it would have taken weeks to get there from page 45, so I scrolled down. It seems that is just keyboard shortcuts for what I clicked manually following this youtube video at 13:46.

Neither way works. Is it because my page lookes different, is timeline? At an earlier stage before the fairlight page, I was able to loop, but not here following these directions.

that video had a lot of clips and I was trying to loop part of one as he shows.
Now I tried a shorter video with only 3 clips and selecting a part and I see what is happening as I can see the whole strip, It goes to the end of the last clip and starts over. Each clip has its own in and out set by trimming.

Based on the screenshot you appear to be on Windows, so you might want to double-check what shortcut they are using for Playback -> Play Around/To -> Play In to Out - on the Mac it is Option+/ and that works for me.

Not sure offhand if they assigned something different to that on Windows... but that is the command you want to use to start playback looping over the selected range (after turning looping on).

I have to close the EQ window and back up.

As an aside, navigation works with the effect window open.

I came back to this again, trying use learn in nose reduction, as well as EQ. Now I selected in and out for a section, loop is on, I used alt / , control /. Nothing makes it loop a selection. I loop back to the beginning of the timeline.

The keyboard shortcut for "Play In to Out" (default: Option Forward-slash), with looping enabled, always works for me to loop playback over a range... if that specific keyboard combo doesn't work for you then you might want to double check your keyboard customisation mapping.

So I looked for a video of looping a section to follow exactly and saw at the last step where he selected 'play in to out' and saw that the menu showed alt /. But in my menu it was blank. So for some reason the default in mine was nothing. So I changed it to alt /. and now it works, thanks.