Same here for netatmo - ironically I replied to an incident report with netatmo saying all was OK when the whole system was falling over.

However netatmo does need to have a server to store data as you need to consolidate acreoss devices plus you can query gfor a year's data and that won't and can't be held locally.

It could be local-first. I don't mind the cross-device sync being done centrally, of course, but the app specifically asks for access to Home and Local Network. I wonder if Home Assistant could deal with blackouts…