iPhone 8 Plus camera autofocus instability

Having upgraded from an iPhone 8 to an 8 Plus I find it much harder to take photos, particularly of items within approx. 0.5-2.0m. The reason is that the phone's autofocus appears to jump in and out of focus and never settle on whatever portion of the image I tap. There's no fault with the lens as I am occasionally able to take a reasonable photo by luck, but most are blurred.

Please note that I have already seen: If the camera or flash on your iPhone, iPad, or iPod touch isn't working - Apple Support

Is anyone aware of any means to fix this. Perhaps there is a third party camera app which might allow manual focus and not cost a fortune, require a subscription, or have invasive data collection?