I expect it's accurate to say; their architecture is not like a database where you can add an index on a blocked state and then join against it. You have to get a list of potential posts that the user might want to see and then eliminate any in the block list. There will be a few edge case users who have thousands of block entries and a multithreading strategy is likely required to swiftly filter it in a reasonable timeframe.
However, an architecture I've seen that works around this is to build this timeline in the background and present it to the user from a cache, I don't know if this is what Twitter does as I never worked on that. However, if you want to not have a block feature but have some kind of mute feature anyway I don't see how there is a meaningful difference.
It is yes, but there is an (unrelated) Android client called Jerboa if that is the OS you use.
I would very much like the Apollo developer to do this but possibly he's burnt out on social media and would like to work on something else. He has developed a series of other unrelated apps that make him a decent income also.