Hi there,
HTML Tables just aren’t natively responsive, and the core Table Block doesn’t provide options to make it so. The best option is to use a plugin like Table Press which adds that functionality.
Other then that the most we can provide is some CSS like this:
@media(max-width: 600px) {
.wp-block-table {
overflow-x: scroll;
}
.wp-block-table table {
min-width: 600px;
}
}
This will force the table to be sideways scrollable on smaller screens – adjust the 600px to suit.