This link is to the manual as at 20 April 2020.
Perhaps you already have this in C:\Program Files\Xara\Xara Designer Pro+\HelpAndSupport\ENG\ as XaraDesignerProPlus.pdf?
I cannot remember if I put mine there or Xara included it in the install.

In the same folder is xarax.chm. Mine is dated 26 May 2021 so is up-to-date to version 21.3 and covered all addition/changes from v20.0 of 04 June 2020.

As a bridge, I have also downloaded the Pro+ Release Notes: http://releasenotes.xara.hosting/designer-pro-plus/ to the same folder. [via Import from Web into Xara > Scroll with PDF button - crude but a stop-gap]
@Xara - The big Download button returns a 404 though: http://releasenotes.xara.hosting/des...s/xr_files.txt has no Pro+_ReleaseNotes_Public.pdf present.

In the meantime, you could try https://pdfcandy.com/chm-to-pdf.html with xarax.chm. This does not create an index but PDF searches do work well.

Acorn

P.S. Moved to Dear Xara Forum