Pressing The E Key On Any Horse No Matter The Version Will Open The Horses Inventory. Easy Way To Work Around This Is Either To Place An Item In The Offhand Slot Before You Ride The Horse Or Use The F Key When Hovering Over The Item You Want In The Off Hand Slot And It Will Switch.
Yes, This Is Intended
Very similar situation to Jeff Derksen. Running arch linux using the latest minecraft-launcher package on the AUR. Didn't have the issue before migrating minecraft to use my microsoft account. This issue is not present on windows for me