Shooting down a spy satellite would be a huge escalation, an act of war. The balloon/objects were shot down in US/Canada airspace. Shooting down unauthorized aircraft is allowed by international law. China also hasn't claimed the later two objects.
Space is regarded similarly to international waters. Spy satellites are free to overfly countries.
Counter space unlikely, but there's no international treaty stipulating where air space ends except fl600, US shooting down PRC assets at fl600+1ft gives PRC openning to mess with US intel gathering in PRC EEZ where at least international law has interpretations for such activities being non innocent passage. I'm not sure if it will get that far since those activities are done by mostly manned platforms, but wouldn't rule out another EP3 tier event or PRC taking more US subsurface monitoring infra in SCS.
Space is regarded similarly to international waters. Spy satellites are free to overfly countries.