There are four trial versions. ZBrush 2019, ZBrush 2020, ZBrush 2021 and ZBrush 2022 . Each is good for 30 days.
Installation Video

Key for 30 Day Trial:
G74D-4H2Y-95W2-GW72

Key for 30 Day Trial:
A517-47WE-A5G3-7139

Key for 30 Day 2020 Trial:
GPKM-5X52-82P6-MZT6

Key for 30 Day 2019 Trial:
GPKM-5W63-82N6-MZ56