You can write about whatever you want. If your main character lives in a cottage in the 1750s with no electricity, but there's a shower for them (made by magic, or fairies, or lowered by ogre blood), you can do that. You can do anything.

Also, who said historical fantasies can't have a little electricity? Are you here for the lover trying to revive her beloved dead by marrying the king of the swamp or for the shower?

If my witch follows the voice of her charmed pocketwatch into the woods to find her blind, telepathic sister, why are we worried about the electric shower?

And why do we stick with 1700s-1900s cottagecore? Why can't we imagine cottagecore in the 3000s?

... I just want my devastated, heavily dressed Victorian maidens to take a shower and not lose a star over it.