As title, I have found a way to increase the PS5 motionplus controller intensity.

Open regedit and navigate to:
HKEY_CURRENT_USER\Software\Sucker Punch Productions\Ghost of Tsushima DIRECTOR'S CUT\Input

On the right hand side, look for the top entry named:
dualsense_emulation_vibstrength

This will be set to 6, no matter what you select in game it will still be set to 6, I set it to 9 and the intensity is much stronger.

Make sure when making the change to chose decimal, not hex.

Maybe a bug on my end but changing the option in game did not alter the value from 6 and once set to something else it doesn't change either, this setting seems independent to the in game setting for some reason.