iOS 10 remember to "not trust this computer"

Solution 1:

Unfortunately, iOS 10 cannot remember untrusted computers.

From Apple support document HT202778:

If you choose not to trust a computer, you block its access to content on your device. You'll see the trust alert every time that you connect your iOS device to that computer.

There is a way to avoid the dialog every time you connect — blocking the data connection while still allowing the USB power connection. You can do that with either (1) a so-called "USB condom" (SyncStop, Juice-Jack Defender, PortaPow) or (2) a "charge-only" Lightning cable.

Solution 2:

I know your question was for macOS, but a few of the other Windows related questions for doing this got erroneously marked as duplicates of this question.

Here are the steps for Windows 10:

Step #1. Connect your iPhone/iPad → Head over to the Control Panel.

Step #2. Click on Hardware & Sounds → Click and open Device Manager.

Step #3. In the Device Manager window, you should see a listing that has the name of your iDevice.

Step #4. Right click on iDevice’s name under "Portable Devices" and click on Properties.

Step #5. Click on the Hardware tab and then click on Properties → Go to the Driver tab → Click on Disable.

Source: Option #3 on this page https://www.igeeksblog.com/how-to-stop-trust-this-computer-message-in-ios-7-on-iphone-ipad/