On macOS the upgrade Task for PioCore doesn’t load the development version.
It seems that the setting "platformio-ide.useDevelopmentPIOCore": true doesn’t work.
This is a known issue and I’ll fix it later. When you stay on a stable release, pio upgrade command will update only to a next stable release. However, it works very well when you stay on a development version.
A temporary solution is to run one time this command in PIO IDE Terminal pio upgrade --dev.