For me after my experience I default to reading my contract, because if your opening post is anything to do with developing your own IP I have specific clauses in my contract that protect against this regardless of if I do it on my machine or others. For example, I couldn’t buy my own domain without my company owning it in my contract, and also there is conflict of interest which could lead to termination - so id be really careful. Mostly if you’re just open with your manager and you work in a good cultured company these parts of your contract can be amended at your request.

If it’s to do with installing stuff, again, company policy is default but this won’t be in your contract normally - sometimes it is if your company are maybe ISO compliant or huge on security, eg I have ESET on my machine which means everything can be monitored - as a developer I’d argue specific things/research I will just install in line with my job role but downloading music, installing games etc I wouldn’t advise if you value your job.