I'll teach you how to set up flight modes in betaflight and cleanflight. You can use a switch to activate Angle Mode, Horizon Mode, Air Mode, the beeper, and any other flight mode you want. The same process can be used to set up switch arming too, which by the way, I do recommend.
I'll be using my FrSky Taranis for this example, but the same procedure can be used with any other common transmitter, such as Spektrum or FlySky. The only difference will be in the steps for assigning the switch to an Aux channel. Sorry I can't help with that if you don't have a Taranis.