[How to Export my own Preset?]

hi i have affinity photo on a imac and i want to Export my own Preset. i spend hours to modify a foto and i like the style and i want to apply to other foto in the future... i must export a "lut"? 

thanks

 

p. s.

i have a new imac 24 (high model with 16gb ram and 80gb ssd free) and i see that the app is a little lagging after more layers (15-20)..other experience? i have ever read that world very good with this new imax