Secure deletetion of files
Im currently using a Macbook Air with a SSD. I have used the machine for work and are now planning to sell it.
However, some of the work related files are strictly confidential and I need to be sure they are deleted.
I’ve done the classical noob-move and have moved them to trash and then emptied the trash bin. But during may best effort googling the matter it seems like there are billions of third part programs who can recover the files. I think it was like High Sierra or something that hade the secure empty trash option which is now removed.
Follwing link: https://www.macworld.com/article/3005796/how-to-replace-secure-empty-trash-in-os-x-el-capitan.html
Gives an option where one can use the terminal but if I understood the article right it only works for HDD?
So, is there anyone here who know a way where I can be certain the files that I have “deleted” are actually deleted or should i just give up the idea of selling the computer?
Thank you in advance!