IMO I don't believe Magui and Lando are PR, or that what she did confirms anything.
I think they just have a dysfunctional, on and off open relationship or FWB situation. Magui is messy, desperate and wants way more out of whatever arrangement they've got going on (like paddock walks, him posting her on Instagram, etc) than he's willing to give. Lando doesn't get anything from faking a relationship with someone with the reputation of being a racist and serial cheater. I don’t know why he’d go along with it just for Magui's benefit
I think Lando just sees her as convenient fun and sex because he already knows how much he can get away with and how much she'll tolerate. Magui is obviously messy AF, but I also don't think particularly highly of Lando in the relationships department either