I'm almost certain that there isn't any laws which governs Bitcoin mining? Certain sanctions might prohibit firms based in the US from handling certain transactions but I don't think they have yet to implement it on Bitcoin mining, because it's just ineffective. Seems like they were just doing so to appease the US government. Do CMIIW though.
Someone living in US and familiar with US law should comment on this, I'm just quoting their own claims that they did what they did based on "U.S. regulatory standards"
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Anyways, doesn't matter. There isn't any reasonable way to prove that they're not censoring transactions anymore.
It is actually easy to prove with a good level of certainty. It just costs a little bit of money in transaction fees.
What we can do is first figure out what transactions exactly they "censor", for example CoinJoin txs. Then choose a time when fees are low, like now that they are 1 sat/vbyte so that it doesn't cost a lot. Then every time a new block is mined (by someone else) we send a couple of such transactions with higher than normal fee to the mempool so that they are definitely picked up by miners but we have to repeat it since MARA pool has lower hashrate and can not find blocks regularly. After they found a block we can see if it contains the said transaction or not. Repeat it a couple of times to avoid false positives.
In other words if the mempool contained a certain type of transaction with high priority fee and a mining pool ignored it when they found a block that means they are censoring that transaction type, otherwise if 99% of the times they are picking that tx up they aren't censoring anything.
