Or if you're willing to take the gamble. My default response to C&Ds (and other similar notices) that have no actual legal justifiability behind them is a nice succinct "fuck off", and I've yet to receive any follow-up from about a dozen such interactions.
Now at least some of those "legal notices" were clearly from people who had never interacted with a lawyer in their lives (my personal favourite was someone who insisted that having their username on a ban list for cheating in a video game was a violation of the GDPR), but there's a lot of entities who have a track record of spamming anyone they can find with vague threats in the hope that some people will cave in to their bullying, fully aware that they can do absolutely nothing to those who don't.
I'm no expert on Japanese trademark law, but I suspect it's very unlikely that Clubhouse has any case here.
There is no viable alternative for a company wishing to publish an app: you have to target iOS or you perish. Many companies today need to have an iOS app. For example, a bank, or a big chain grocery outlet, probably needs an iOS app to exist in the market. This isn't a tiny niche area which can be avoided.
The only way you can publish an app is with Apple's approval. Therefore, Apple are exercising a significant degree of market power.
In the US, the idea that because a company is private it can trade however it pleases has been rejected since 1890 when the Sherman Act was introduced. It's the same in most capitalist economies. The conduct of companies is subject to reasonable regulation to ensure healthy competition.
I've established earlier that Apple has significant market power in the mobile app space. Because of that, it's fair that we ask Apple to be reasonable when deciding what apps to approve, and the conditions on which they approve them, because they are exercising a significant degree of market power.
This is a space calling for regulation. Apple and Google should not be free to reject or impose conditions on apps as they wish. We have a right, as the people who make rules about how companies may trade, to ask for them to be regulated when they are exercising a significant degree of market power.
The viable alternative is a web page. But yes, if you want the security and performance supported on a native Apple platform, you have to play by Apple's rules.
Harm to companies isn't harm to consumers.
And harm to companies is harm to consumers when they purchase products with applications that get taken away due to Apple (example: I upgraded my iPhone to play Fortnite, which was available on iOS at the time of purchase -- now it's not).
They have only been consistent in having a walled garden. Their rules have been inconsistent in how the rules are applied.