Is possible to delete files in cloud on my Mate 20?

If your Gallery has the “Sync Gallery’ turned on, when you delete the photos from your phone, you’ll get a prompt to ask if you want to delete the copies on the cloud as well. Make sure you have this option selected to have the cloud copies removed as well.

Then the files or docs that are saved to Huawei Drive, you can go to the Files app > Huawei Drive to delete them from there.

If you’ve the cloud backup turn on, you can delete your backups that are saved in the cloud by going to Settings > Account center (first option) > Cloud > Cloud backup to select the backup that you want to delete.