Is there a way to force variant by user agent? I see a

browser

override rule, is that checking user agent? If so, can someone check my regex syntax?

It's up to you which attributes to pass into the SDK and use for targeting.

browser

is a default one, but you can delete that and use something more specific like

isTesting

. Add/remove attributes on the Features -> Attributes page in GrowthBook. Then, update your SDK integration to pass the new attributes in.