A year ago China would be interested in buying ARM. Not anymore IMO.
China seems to like/want to control things. E.g. The Huawei/5G infrastructure equipment market.
So, I think they could still be interested in arm, as it would give them a bigger stake/control of the wider technological (especially electronics, mobile phones and computing) fields. It also, would make it harder for possible future sanctions to be placed, in the future.
Arm (presumably), gets all sorts of information, about what is going on in the electronics world, on a world-wide basis. Because so many things have arm chips in them, these days.
That information, could be very valuable to Chinese electronics interests, as it is giving them (sometimes very) advanced knowledge, about what is happening in the future, as regards the electronics/technology sector.
But, just as you were, I'm voicing my own opinion. Also, China could be interested, in the significant number of cpu (and similar), expertise. that arm employs and has built up, over a long period of time.
Especially, as existing trade sanctions (if I understand correctly, from the US), prevent the better cpus available, from legitimately being sold to China.
So, China have been trying to produce their own, home grown cpus, for use in super computers, e.g. for doing giant nuclear weapon simulations. Because the Intel server chips (maybe high end only), were barred from being sold to China (exported), because of US military trade restrictions.