Burning BDXL discs, does the entire disc have to be burned in the same session

I really do not know anything about burning, so please bear with me.

I’m planning to save data that I want to keep forever to BDXL M-discs that are 100GB, and it would be really helpful if I can burn each one of these across multiple sessions.

Can I burn these 100GB across several sessions, or do I get only 1 burn, and thus should try to fill the 90 or so GB as much as I can in the one burn?

Problems I’ve had in the past with 8GB DVD-R’s is that I burned something like 2GB, and then when I try to burn more to the DVD-R, the software thinks it’s full when I only burned 2GB previously. There should have been at least 5 more GB of effective disc space to burn.

That was a long time ago though. I’m just concerned about these uber-expensive M-discs.

Thank you

Oh, and I forgot to say, if it is possible to burn to a bdxl across multiple sessions, what software allows for that?