Touchscreen on HP Envy x360 is not working with 18.04
Solution 1:
There are two options as for now, both of them presented in following link: https://bugzilla.kernel.org/show_bug.cgi?id=198715#c14
The first option is to patch kernel manually and install it on your system, I've tested it, it works for my HP Envy x360 15-bq121dx.
Another option is to patch acpi table, people in discussion in link above report successful result. I haven't tried this method yet.