James, welcome to TalkGraphics.

in reply:
1. No one knows. Probably not even Xara who have yet to explain anything about bug fixes, versioning or upgrading. As an outsider, it certainly looked like a cobbled-together response as the lack of marketing of v20 or a trial version puts it on its own island of destitution.
2. No one knows. You v20 Perpetual will be forever. You will not lose its capability if a "v21" comes along. If a v21 appears, it will probably use the same licence that you have for your v20. This means you will be limited to two active downloads of a mix of v20 & v21 on your system(s).Whether you can install v21 and later on revert to v20 is another Xara question. 'Forever', in reality, means it will run on Windows 11 and lower to 8.1.
https://www.xara.com/designerpro/v20/ :: While V20 is our latest offering, we plan to develop future versions that incorporate new features, enhancements, and the latest design trends. There are no dates or plans set for a future version. If you require the latest features, updates, and constantly updating design content, the Plus versions are updates on a regular basis.
3. I have a new Huion Tablet, Inspiroy Ink, but I have noticed this too. That said, I am no digital graphic artist or designer. I use the Shape Painter Tool mostly and don't get the wibbles. Using the Brush Tool, I set Pressure recording and so get the Pen Pressure profile. Beyond this, I am a tyro.
4. I would like to understand more around your 'tweaking'. You need to describe your machine first off as I have never done that much to get Xara working with thousands or nodes.

Acorn