What are your Windows Version and Build Numbers? There is a change in ALT+TAB default behavior with the introduction of Version 20H2 and I suspect that's what's going on. The settings you refer to have nothing to do with ALT+TAB behavior.
I don't want to get into the 20H2 "change back" steps unless I know you have 20H2. --
Brian -Windows 10 Pro, 64-Bit, Version 2004, Build 19041
The purpose of education is not to validate ignorance but to overcome it. ~ Lawrence Krauss