unable to power-off new ipad mini 6

Just received my new iPad Mini 6. Slight problem, unlike previous models (my old iPad Mini 5 for example) this new one will not power down. I hold down the power button, but it never presents the slider bar so I cannot turn it off. I've wasted an hour searching online for a way around this problem but apparently no one else has attempted this. I'd really like to turn it off before installing the SIM card; that's the way I've always done it.

Thanks in advance for any advice! Oh, as usual, I'm unable to select the actual device I'm talking about because it's not shown, so I chose iPad Mini 5 instead.