I think there is no need to compress the KRA-File, at least we transfer and HiDrive accept huge files AND these services are free of charge.
And if libre means non-trackable for you, you can use
they don’t ask you for any information you have to click the upload file button, choose your KRA-File and will get an address from where to download your file - you can register with them, but you don’t need to. I have friends who live in a Southeast Asian dictatorship and rely only on this service. If you want to be absolutely sure that only the recipient can use your file, you could upload it in a password-protected archive and send the key for it separately via PM.
Try it with this free background made by me:
https://anonfiles.com/fbWbu6Vdu7/BACKGROUND_2_7z
Pass: em@il4YOUReyes0nly
Michelist