iCloud seems to be very slow when uploading images why is that so?

Typically Internet plans have lower ‘upload’ speed (sending files to the cloud), than ‘download’ speed (getting files from the cloud). Have you run something like ‘Speedtest’ to see how much upload speed you have? This will first tell you if you’re getting what you’re paying for, but also whether what you’re experiencing is abnormal (it might take a little math to figure this part). Another question would be whether you’ve used other cloud services and whether they are different in uploading than iCloud?

There are also other variables like congestion during busy times of the day, but the above assumes you’re getting ‘slow’ performance all the time.

I have the same issue.

Every iCloud service is very slow.

If I'm using One Drive oder Lightroom there is no problem.

I think it doesn't depends on my connection speed.