You have too many (10+ lol...) TWinControl on form and trying resizing width or height ... It's really crazy in 2020. Internet browsers resize 10000+ controls with no lag because there is no WinControls (only one main form) ... but resizing 10+ native WinControls lags ass hell ...
LCL layout engine is fast. You can resize 1000+ non TWinControls with it (eg. TShape, TLabel , ...etc. ).
Try to eliminate all TWinControl based controls ...