[all variants] Encryption of an external hard drive used also with Windows or Max OS

Hi.

My search in the forums on this topic has retued nothing so I start this thread.

I have an exteal USB hard drive which I use with my laptops (ruing Ubuntu or Linux Mint) but also with other computers ruing Windows. I might have in the future to use it with Macs.
It is currently NTFS formatted although reformatting it would not be an issue.

I wish to protect its content by encrypting it. A few years ago I would simply have used TrueCrypt but since it is not supported any longer, I am wondering if I'd better not search for another solution.
Creating a LUKS partition would not not work with Windows OS. Similarly using BitLocker would not work with Linux.

Any idea ?