To get an HFR value, you need to have the FITS option "auto-compute HFR" set before capturing the image (it doesn't recompute already-captured HFRs
it as it currently stands). If you did that, then click on one of the captures, and you should get a positive HFR value in the HFR value box.
If you have HFR values, then you should be able to get a plot. The simplest way to see it would be to disable all the checkboxes except for HFR.
You should see flat blue lines on the graph, corresponding to each capture on the timeline. (You can then enable other plots, if you want).
You can use your mouse/scroll-button to zoom in to the right scale when pointed over the plot window near one of the HFRs.

Let me know if that doesn't work.
Hy

Unfortunately this is not working for me. After click on green bar representing exposition, the Details tab is not containing HFR value, even label for it is not there. Also Filename is empty (but label is there). So it looks like the Analyze function does not know where to look for physical files, and so it cannot read the HFR value from FITS header.

Analyze works a bit differently than what I understand you to be saying. Analyze does not read HFR values from the FITS header. Instead, during the Ekos session, it records the messages that are passed back and forth between the various processes, and stores them in a .analyze file. If the HFR is not computed during that session, then the values won't be recorded, and won't be displayable in Analyze. Unfortunately, if you want to see an HFR graph, you need to have the auto-compute HFR checkbox set before you capture the images.

Ok, I see. I have enabled that auto-compute HFR checkbox prior execution of capture, but still not able to see that values. What else can be wrong? Can someone please confirm that this works?

Now it works. As you mentioned that it records the messages, I realized that your code is probably reading HFR messages from FITS viewer once it is opening captured image. I don't use FITS viewer in this way, so once I enabled FITS viewer, the HFR value is now displayed in the plot. Thank you hy

I'm looking at the code now, and it looks like fitsviewer needs to be running for all that to happen.
Do you not use fitsviewer?

If you do, please post a log file with at least fits and capture debug logging set. Also send the corresponding .analyze file (which is stored in a sister directory to the log fils). For instance, on linux the log files are stored in ~/.local/share/kstars/logs and the analyze files stored in ~/.local/share/kstars/analyze.

Hy