Sailfish X version 22.214.171.124 (and any earlier, probably some of the later, too) has the issue that although WLAN hotspot (a.k.a. internet sharing) can be enabled in the UI (Settings > Internet sharing), Xperia X device does not provide any WLAN network for other devices to join.
For now, the issue can be circumvented with the following commands. This requires that the device has the Developer mode enabled and the SSH password set.
devel-su echo 2 > /sys/module/bcmdhd/parameters/op_mode
Restart WLAN from UI ("Settings > WLAN") and enable hotspot ("Settings > Internet sharing")
ip link set dev wlan0 master tether
The WLAN network configured in "Settings > Internet sharing" should be available now.
echo 1 > /sys/module/bcmdhd/parameters/op_mode
Disable hotspot and restart WLAN from UI.