Muddle together strawberries and sugar in a large pitcher or mason jar. Allow mixture to sit for 5 minutes. Stir in apple cider vinegar and balsamic vinegar. Cover and let mixture steep in the fridge for 2 days. Strain out strawberry bits and discard. Store syrup in the fridge until ready to use.
Add 1 oz shrub syrup to a serving glass filled with ice. Top with chilled sparkling water. Stir to combine. Garnish with fresh strawberries, if desired. Enjoy immediately.