自分も404問題に悩んでたけれど
広い検索バーをオンにせずとも解決した
何が奏効してるかは不明なので一応設定を貼っておく
==================
"close_interstitial_ads": true,
"default_playback_speed": 1,
"default_video_quality_wifi": 1080,
"disable_ambient_mode": true,
"disable_auto_captions": true,
"disable_haptic_feedback_chapters": true,
"disable_haptic_feedback_scrubbing": true,
"disable_haptic_feedback_seek": true,
"disable_haptic_feedback_seek_undo": true,
"disable_haptic_feedback_zoom": true,
"disable_hdr_video": true,
"enable_external_browser": false,
"enable_save_video_quality": false,
"enable_tablet_layout": true,
"enable_tablet_navigation_bar": true,
"external_downloader_package_name": "org.schabi.newpipe",
"hide_account_menu": true,
"hide_account_menu_filter_strings": "作成した動画\n映画とテレビ番組\nYouTube Premium に登録\nヘルプとフィードバック",
"hide_audio_track_button": false,
"hide_button_create_clip": true,
"hide_button_remix": true,
"hide_button_report": true,
"hide_button_rewards": true,
"hide_button_thanks": true,
"hide_button_transcript": true,
"hide_comments_thanks_button": true,
"hide_community_posts_subscriptions": true,
"hide_create_shorts_button": true,
"hide_feed_flyout_panel": true,
"hide_feed_flyout_panel_filter_strings": "キューの最初に追加\n報告",
"hide_game_section": true,
"hide_mix_playlists": true,
"hide_movie_shelf": true,
"hide_notifications_button": true,
"hide_notify_me_button": true,
"hide_player_flyout_panel_ambient_mode": true,
"hide_player_flyout_panel_lock_screen": true,
"hide_podcast_section": true,
"hide_search_bar": true,