Universal Disk Format (https://en.wikipedia.org/wiki/Universal_Disk_Format).
I can confirm it works on Linux, and works on Windows (at least W10). The wikipedia article indicates it works on newer MacOS'es, but I can't confirm that fact.
Yet, it seems there's no way to format to it out of box on macOS and support looks dodgy. I'm not willing to bet my data on an unreliable file system implementation.
Nope, although it is most commonly used on optical media it is not restricted to only optical media.
From the wikipedia article:
Specifications
The UDF standard defines three file system variations, called "builds". These are:
Plain (Random Read/Write Access). This is the original format supported in all UDF revisions ... Plain build
Introduced in the first version of the standard, this format can be used on any type of disk that allows random read/write access, such as hard disks, DVD+RW and DVD-RAM media. Metadata (up to v2.50) and file data is addressed more or less directly. In writing to such a disk in this format, any physical block on the disk may be chosen for allocation of new or updated files.
Since this is the basic format, practically any operating system or file system driver claiming support for UDF should be able to read this format.
I have had zero issues with it from Linux or Win (I think I started using it when the "work pc" was Win7, but am not 100% sure of that). It has just worked, with no problems, for my use cases.
Performance wise, well, the performance is limited by the USB sticks (they are USB2 sticks) so from what I can tell, UDF is not the limiter, the USB2 interface or the flash cells in the stick are the performance limiter.