Best alternative to Photoshop ?

I'm not willing to pay a subscription to Adobe when I only use an image editor occasionally.

Definitely need a 'user friendly' interface, good selection tools, feathering and airbrush painting.   Also need online tutorials... (YouTube?) 

I have identified these but not sure which is best or if there is a better alternative....

PIXELMATOR Classic      £28.99         www.pixelmator.com/tutorials

AFFINITY PHOTO    £23.99      (YouTube online tutorials??)

LUMINAR     price ?       (YouTube online tutorials??)

( I have Photoshop 6 on my old MacBook but it won't work on my new MacBook Pro running Big Sur OS.  And I aim to sell the old MacBook )

I'll pay up to about £35.

Thanks