Yes Clipchamp includes 4k video conversion support for most 4k file types.
If you have a 4k video and want to compress it to 4K at a smaller file size, select it as the input file and choose "keep resolution" as part of your output settings. This will convert your 4K file to a 4K MP4 video which is going to be smaller in file size than the original at no visible quality loss in most circumstances.
The converted 4k video can be uploaded to YouTube, Vimeo, Facebook or Google Drive straight from within Clipchamp.
4k video conversion works in Clipchamp in Google Chrome and Opera.
If you'd like to upload 4k to YouTube without the large file sizes and seeing that the iOS YouTube uploader for instance reduces 4k videos' resolutions automatically before uploading them to YouTube, saving these videos from your iPhone or iPad to your computer and using Clipchamp to compress them without losing the 4k resolution and then uploading to YouTube is the better alternative.
If you want to obtain a smaller resolution output video, select your 4K video as the input and pick any of the options other than "keep resolution" in your output settings. Available options are 240p, 360p, 480p, 720p and 1080p.