In order to have RTL mode enabled, you need to import below rtl scss files in the index.scss file src/design/app.scss.
@import "custom/rtl/bootstrap-rtl";
@import "custom/rtl/components-rtl";
@import "custom/rtl/float-rtl";
@import "custom/rtl/general-rtl";
@import "custom/rtl/pages-rtl";
@import "custom/rtl/plugins-rtl";
@import "custom/rtl/spacing-rtl";
@import "custom/rtl/structure-rtl";
@import "custom/rtl/text-rtl";