Use # instead of v-slot:

src/client/app/mobile/views/components/ui.vue

@@ -1,7 +1,7 @@
 <template>
 <div class="mk-ui">
 	<x-header>
-		<template v-slot:func><slot name="func"></slot></template>
+		<template #func><slot name="func"></slot></template>
 		<slot name="header"></slot>
 	</x-header>
 	<x-nav :is-open="isDrawerOpening"/>

src/client/app/mobile/views/components/user-timeline.vue

@@ -1,7 +1,7 @@
 <template>
 <div class="mk-user-timeline">
 	<mk-notes ref="timeline" :make-promise="makePromise" @inited="() => $emit('loaded')">
-		<template v-slot:empty>
+		<template #empty>
 			<fa :icon="['far', 'comments']"/>
 			{{ withMedia ? this.$t('no-notes-with-media') : this.$t('no-notes') }}
 		</template>