Since Mastodon (and the wider fediverse) doesn't deal with shadow banning and proprietary algorithms, hashtags can still be useful!
One I will try to contribute to and invite others to is #MeltICE
I envision #MeltICE to be specific to examples of people resisting ICE. It can also include strategy, reflections, report backs, etc
For general talking shit on or exposing the horror of ICE I encourage folks keep using #FuckICE and #AbolishICE