You need to ask your DM inbox relays to delete your inbox. Super easy.

is the desire purely organizational? im sure to would be easy to locally archive chats

Also NIP17 groups are IMO quite problematic when it comes to gaslighting. nostr:nevent1qvzqqqqqqypzpg78lsd0mrjnpljpa54n6u36dkxg03yh8hp4zhaesz2cwetgyahqqy88wumn8ghj7mn0wvhxcmmv9uq32amnwvaz7tmjv4kxz7fwv3sk6atn9e5k7tcqyr8htrves080538chlp6dpr3wvdk7rxmrsjvp9dkmq6823lyflep6d3upqn