Icons on the home page are VERY small since the iPadOS 15 update

From iPad settings:

Settings > Home Screen & App Library > Use Large App Icons - set to ON

If this setting does not resolve the problem, please share a screenshot - redacted if required using markup tools to remove personal or sensitive information:

Take a screenshot - Apple Support

You can post your screenshot using the image button at the bottom of the editing window:

I refer to the message editing window that you are using to participate here.

When selecting the saved screenshot image from your Photo Library, you'll see a blue Options button at bottom left of the selector window. Tap Options and choose Medium - or if necessary, Small - then select the screenshot.

Alternatively, simply crop the screenshot to reduce the overall area of the image - leaving a representative area to show the relative size of App icons on your Home Screens.