I have a rhizomatous begonia (B. ricinifolia 'Immense') that's growing out of its pot. It was a small-medium plant given to me about 3 years ago, and now it's huge!

It lives right below a bright south-facing window. Not really any issues, though some of the lower stems get floppy and fall off the rhizome occasionally. The plant is also really tall now, so I'm thinking I need to place it higher in the light.

But the rhizomes are growing off to the side and producing leaves, and I worry it'll tip the pot eventually. I think I read you can cut the rhizomes and plant them, but I wanted to get advice before I mess up my plant. I repotted it a couple years ago, but the whole thing went floppy in the couple minutes I had it between pots. It took like 2 days to stand back up and I thought I'd killed it. So dramatic! So I'm not trying to upset it too much. Should I cut the rhizomes and start a second plant, and if so, where to cut? Should I repot the whole thing in a longer container? Prune it in some way to change its habit? Is the rhizome growth due to stretching toward light, or is that normal?

Thanks!

Hi, can you add another picture? Back up and show the whole plant?

You can trim the rhizomes and lay them on the soil surface.

Here's a wider view of the whole plant!

It might like to get a little closer to the window but looks great to me for an indoor plant. There are some plants in the database on this site to compare to yours:
Begonia (Begonia x ricinifolia)

They do that, you can prune them back and use the cuttings to propagate more plants if you wish.