It seems that pressure.js is not compatible with Chrome on Ubuntu. Here is my detailed configuration:

• Chrome 86.0.4240.75 (Build officiel) (64 bits)
• Ubuntu 20.04 (5.4.0-53-generic)
• Wacom INTUOS 4 (properly configured, pressure works fine in other softwares like Krita)

I also tried with Firefox 82.0.3: same result.