Honestly, I don’t know - I haven’t fiddled with the themes much on my Linux installations. All I can say is that currently, for the 3.x series, out of the box VLC looks very similar between Windows, Debian (KDE Plasma) and Linux Mint (Cinnamon) - all three of which are arguably different DEs.
A couple of other comments have flagged that this is the new 4.x UI, which certainly explains the difference.
Doesn’t it use whatever theme you have your DE set to by default?
Honestly, I don’t know - I haven’t fiddled with the themes much on my Linux installations. All I can say is that currently, for the 3.x series, out of the box VLC looks very similar between Windows, Debian (KDE Plasma) and Linux Mint (Cinnamon) - all three of which are arguably different DEs.
A couple of other comments have flagged that this is the new 4.x UI, which certainly explains the difference.