It seems if you are using a Magic Keyboard made from Apple, it’s better to have Full Keyboard Access off. I experimented with deactivating the command (and several others) that overrides the spacebar but the issue was still present in some apps and in terminal. Only when FKA is totally turned off does the spacebar function come back on my iPad Pro (iOS 15, iPad Pro 11in Gen 2). Also from what I’ve experienced, the Magic Keyboards (w/ numpad) loose no functionality when connected to the iPad while FKA is off. Hope this update helps others. Basically; Apple Magic Keyboards: turn FKA completely off 3rd party keyboards: disable the “activate” command