Then I generated sql statements to remove duplicate posts that had higher ids than the other posts theyre a duplicate of
i assume this was done after updating the other tables referencing this table, such as comments, votes, saved posts, as previously discussed on matrix?
while it may be omitted here for simplicity, it can be dangerous to not mention that for others that might find this in the future if they experience index corruptions on their own if they don't fix all references, as that would result in data loss.
you can only set a community to only allow local users, not prevent users from interacting with remote communities.
you'd have to either disable federation or set up a script to automatically remove all remote communities, but that also won't be a per user thing, just a per instance thing.
fwiw, the estimate number only states the max amount of activities behind. the real number can be lower, but not higher (unless sending is entirely broken on the instance being checked).
each activity being sent has a numeric id in the database. lemmy has an api that returns the id of the last activity that was either successfully sent to an instance or skipped when it didn't need to get sent (e.g. pm to a user on a different instance). there may also be holes in activity ids due to postgres implementation details for auto-incrementing sequence ids.
for determining the highest known activity id to compare it with the last activity id sent to a specific instance, you can just go through the successfully sent ids for all instances in the response and find the highest number across them all. then you can calculate the difference between the highest number and the number for the specific instance.
depending on the lemmy version and timing of the action, it can take up to 30 seconds for the activity queue to deal with new activities, so on a somewhat busy instance the delta is likely rarely going to be zero.
while this is generally what most people talk about when speaking of defederation, admins can also decide to remove communities locally without blocking the entire instance.
at least the image resizing topic has recently been fixed in lemmy, thumbnails sizes are limited (at the time of thumbnail creation) in the latest release. I'd have to look closer at the other stuff, the api part is unlikely to have changed and will affect all frontends, but js part should differ depending on the front end. some instances already use other frontends by default and there is also a replacement for lemmy-ui being worked on (lemmy-ui-leptos), but I don't know how they compare. either.
it should be taken into account though how much of this is cacheable as well, as it will then typically only affect the first load for the static files.
I can totally understand the issues in general though, I've been living with a 64kbps uplink for several years in the past.
based on the creation date advertised by the instance, lemmy.ml exists since 2019-04-20. lemmy.world exists since 2023-06-01.