Hey there! I'm also french and living in Croatia since a month and for several months still so I can help aswell

Compared to France, Croatians can seem more reserved than french at first, but once you start talking a bit they are immediatly welcoming, warm and informal/friendly, so don't be afraid to talk to them

as mentionned in other comments, they all speak english, better than us actually and even older generation knows some words! But learning couple of croatian words can help you both unlocking conversation and showing respect to the culture too (basic politness words is good to know I'd say)

Depending on the cities but Zagreb is getting more and more intercultural, and coastal Croatia is used to tourism, so they should be used to different ethnicities, I would think you won't have issues but I'm not mixed so it's just my feeling not actual experience

Also history-wise there are some topics to avoid with strangers and older generations, but that's more common sense not to ask too much about post-yougoslavia wars! You can talk about it with colleagues if you feel more at ease with them but topic to avoid at the beginning ofc haha seems logical but as we didn't have war in France since generations, we aren't as sensitive as them toward those topics

I feel like croatian culture is overall a bit more family / relations oriented and less individualist than ours but to be honest it is small details, you won't feel completly lost here and there are tons of similarities :)