Make the sweetened condensed milk according to the directions and let cool to room temperature. Whisk in the heavy cream, powdered sweetener, vodka, vanilla extract, and salt.
Taste the mixture and adjust sweetener to taste. You can use additional Bocha Sweet or allulose here but because it's granular, you will need to whisk for a while to dissolve it properly.
Chill the mixture at least one hour and up to overnight, then pour into the canister of an ice cream maker and churn according to manufacturer's directions. If you have the kind of ice cream maker that requires the canister to be frozen first, don't forget to do that!
Transfer to an airtight container and freeze until firm, at least 4 hours.
To make this keto vanilla ice cream without an ice cream maker:
Make the condensed milk as directed. Let cool to room temp and then whisk in the vodka and salt.
Whip the heavy cream with the powdered sweetener and vanilla extract until it holds stiff peaks.
Pour in the condensed milk and fold these two together until no streaks remain.
Transfer to a container and freeze at least 6 hours.