I want to transfer ownership of an iPad without erasing apps. How?

Apps are forever tied to the AppleID used to download them

and that AppleID and password will be required to update

those apps in the future.

You may wish to start with this link:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

What exactly are you trying to accomplish?

Be aware that Apps are effectively licensed to the purchaser - and are permanently associated with the AppleID used for their purchase. If you fully sign-out from your AppleID, while Apps may continue to work, they cannot be updated or reinstalled. If changing ownership, Apps purchased by a different user (with a different AppleID) will be more hinderance than benefit.

If you are transferring the device to a family member, you can selectively share many purchased Apps, subscriptions and Apple services using Family Sharing:

Family Sharing - Apple

Set up Family Sharing – Apple Support

Share App Store, iTunes Store and Apple Books purchases with Family Sharing – Apple Support

https://www.imore.com/how-set-up-family-sharing-iphone-ipad

If transferring your iPad to somebody else, family or otherwise, you should prepare it properly - as this is the only method by which you can be certain that you have removed all sensitive and personal information from the device. Similarly, you must ensure that the Activation Lock is disabled - as otherwise the new owner will encounter difficulties:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support