I was curious too after reading the news, what happens to fractional shares in this case?
I had a fraction of Apple share when they split last year, it was less than 1 share and I believe it was all sold.
If I had to guess I think your 0.29 will be sold and you will gain 3 shares on top of your 1 share. Don’t take that as correct though I could be wrong!
I have less than fraction of a share so will be interested to know if and when Trading 212 would be likely to liquidate my fraction.
I bought Tesla before the split, it was rounded up as much as possible and the fractional remainder was sold at the current market price.