Hi there,
No, the SmartThings application is not necessary for you to operate the oven or use the self-clean option; it offers options to remotely manage your range. For reference, please see the link below and check pages 38-39 (Operating the oven).
User manual:
https://downloadcenter.samsung.com/content/UM/202407/20240724131335393/01._IB_FULL_NE5000A_NE63A6511_AA_EN.pdf
Have a great day,
-Ernest-