Online multiplayer and rankings will no longer work…
“In early April 2024, online play and other functionality that uses online communication will end for Nintendo 3DS and Wii U software,” Nintendo said on its Support website.
“This also includes online co-operative play, internet rankings, and data distribution.”
“if an event occurs that would make it difficult to continue online services for Nintendo 3DS and Wii U software, we may have to discontinue services earlier than planned.”
As for Pokémon Bank
Pokémon Bank will still retain its online functionality (presumably since it’s still used by players and uses online connectivity as its central mechanic).
Yea, of course. Most Monster Hunter games are completely self-contained and can be played solo offline or local co-op (also offline). The older games do not adjust their difficulty when attempting guild quests since those are usually intended for co-op play, so the monsters' health and damage numbers might exceed your current level. But if you're not interested in those, pretty much every Monster Hunter game - including the 3DS titles like 3/4 Ultimate and Generations - has its own offline story mode and plenty of quests to play through.
If you have a friend to play with, local co-op is heaps of fun. Back when the series was reserved to the PSP, that's how I got my hundreds of hours clocked in.
If you do end up trying out any of the 3DS Monster Hunter titles and do not have a New 3DS, do get a Circle Pad Pro if you haven't already. It's essentially a grip for the 3DS that makes the handheld bulkier and adds a much-needed second joystick for camera movement.