Since Bootstrap V4 the hidden-X classes have been removed. In order to hide a column based on the column width use d-none d-X-block. Basically you simply turn off the display of the size you wish to hide then set the display of the bigger size.
- Hidden on all .d-none
- Hidden on xs .d-none .d-sm-block
- Hidden on sm .d-sm-none .d-md-block
- Hidden on md .d-md-none .d-lg-block
- Hidden on lg .d-lg-none .d-xl-block
- Hidden on xl .d-xl-none
Taken from this answer.