TWIC 1276 Caro-Kann
Two Knights 3..Nf6
GRENKE Chess Open 2019 rd5
White came up with 5.a4!? which does not seem to do very much but is not mentioned by Fernandez in The Modernized Caro-Kann(Thinkers Publishing 2018). Black responded with 5..e6N and the game was already in new territory
White has ideas like a4-a5 and/or Nd6
What do you recommend for Black?