All of the Home Cinema rentals are HD, no 4k stream available. There may be reduced bitrates but it may be difficult to see the difference without a direct comparison between reduced rate and full rate.
And many VOD services (Apple for sure, can not say about netflix or amzn) use variable bitrate technology. So even if they have a UHD copy, if network congestion does not allow for it, lower quality encode will be automatically used. And the other way around - if network allows, bitrate will be increased also automatically.