Is it safe to install the new update 16.5.1 in iPad 9th generation?

You should always install an available System Software Update - or Rapid Security Response (RSR) Update - when they are available. These updates include functional and essential security updates for your device(s). RSRs are intended to patch vulnerabilities and mitigate emerging exploits that can compromise your device and/or your data.

At time of writing, iPadOS 16.5.1 current - as is the RSR that patches iPadOS 16.5.1 to iPadOS 16.5.1(c).

See >>> About the security content of Rapid Security Responses for iOS 16.5.1 and iPadOS 16.5.1 - Apple Support

You should note that for your iPad to install an available System Software Update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - or be updated by a PC or Mac using iTunes or Finder - over a USB connection. The only prerequisite for installation of an RSR is connection to WiFi or other network.

is it safe

The update to iPadOS 16.5.1 (c) is safe and recommended for all users.

Also, what are the things I should do before updating my iPad?

Connect the charging cable and/or verify that the battery is charged more that 50%.

Verify that some free space is available for the download of the new version.

Don’t interrupt the update process (after the initial download).

After ANY iOS/iPadOS upgrade/update, you should ALWAYS perform a simple hard reset/forced restart of your Apple mobile device.

For iPad models with a Home button, do a simple hard reset/forced restart of your iPad by holding down both the Home and sleep/wake/power button simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

OR

For much newer design iPad models, without a Home button, try the new simple hard reset/forced restart procedure for the new 2018-2022 iPad Pros, 2020/21 iPad Air 4 and 5, the 2021 iPad Mini 6 and the new 2022, 10th gen base models,

1. Press and release the volume button closest to the top Power button

2. Then immediately ( and quickly ) press and release the volume button farthest from the top Power button.

3. Then, press and hold the top single sleep/wake/power button You will see the Slide to Power off button, but keep on holding down the power button until you see the Apple logo, then let it go.

Once you have performed all the steps, wait for a few seconds and your 2018-2022 iPad will boot up completely to the iPad’s Lock screen.

Tap, read and follow this Apple support link below.

Force restart iPad - Apple Support

Best of Luck to You!