Besides "git gud" and "play offline", what can I do against invading Julianas?
They either:
- invisible and waiting for ambush
- tanky and instadown you with a machete
- jump like crazy, and after taking some damage, retreat and heal

I like invasions, but kinda stuck here. Have problems with detecting her, doing enough damage before she could run away and can't defend against machete. Youtube has only Juliana tutorials. Any help appreciated.

Wait until you have some slabs and know how to slap her down well. Playing against AI Juliannas will give you an idea of what to do as well as some trinkets and slabs.

Other than that hack some turrets, plant them behind a set of doors in a room with an additional exit and vantage point ASAP if you want a bit of an advantage. She will need to focus on the turrets (if you've no slabs to play tricks on her with) while you can pick her off from the vantage point. You can also turn your grenades into mines with the G button which will make things even harder for her if you have a safe area that is completely rigged against her.

Try and make life hard for her. You can also insta kill her with a backstab from a machete. If she's trying to disarm or shoot mines and you drop down from aether and backstab you have a chance. Same goes for shift and backstab.

Playing as Juliana for a bit will also give you insight into other players tactics and make it easier for you to know what to do.

I broke one by spending an hour exploring the map while they camped the Visionary's room until they snapped. I may not have gotten one of the better invaders...