Great Shotcut 19.10.20 (Windows) and previous version has a annoying bag:
If new preset for x265 codec has been created and selected, next x265 CRF option changing (in Codec tab of Advanced panel) is not affect to output quality.
To change real quality, it’s need to edit “Other” tab:
It is working fine for me and many others. You need to try harder if you want help. Do not reply to a solved thread unless your problem matches its description exactly.