The mother banana tree died back last year but the stump is still anchored well in the pot. The baby is 5 ft tall and has been pushed to the side. Can I dig up the trunk, remove its roots to give Baby more room to bloom and grow?

If it were mine I would take it out of the pot and see how intermingled all the roots are, very carefully with your fingers try to separate the roots and see if you can get them apart, just don't pull them apart.
Other members will have more advice for you

Is the reason its not planted out in the ground a space consideration? Just wondering with you being in Houston, it could be planted out.
You can unpot it like Christine said and separate them, you might have to use a pruning saw to remove the old one, but it usually does not affect the pup, this is the way banana plants are propagated all the time, by the corm being exposed and chopped up or a sword sucker pup being sliced off (with some roots) from the adult plant.
If you remove the old trunk and cut it into sections each with some roots and plant them, you may get new plants.
All my bananas are in the ground and we never bother to remove the old corms, but in a pot you will need to make space if you intend to keep it in there

Thanks! @Gina1960 Yes the pot is a space-thing. But as you might guess from my screen name, the entire yard is shady. I have half sunny places out front but it is lawn. So I get the driveway, an only the edges, of course. for some reason Dh wants to park a car there??? eyeroll So this particular pot sits in full sun. Momma banana plant gave us a few bananas and had a baby. The left over trunk is typical? A memorial to Momma?

I do have two of the same banana trees in the back getting morning sun. Houston's morning sun can be harsh, but still, they are the same age, only about 2 ft tall and never reproduced. They just don't get enough sun back there. It's pretty though.

I will dig up the pot before it really starts growing and try to untangle the roots (called 'unapting"?) and get it centered in the pot as it also tends to tip over. Thank you.

Sorry that was a common typo I make, I have a finger drag...unapting is unpotting.

Bananas only bloom once. They belong in the family with Heliconias, Ravenella, Etlingers and other gingers....its a once and done.

The normal life cycle of a fruiting banana takes 18+ months to complete. This is why many people in the USA never get bananas...their natural 18 month cycle does not fit with the 12 month seasonal weather schedule here. Of course you can get bananas if you never allow your plant to lose more than just a few leaves in winter....

In commercial banana production, the hands of bananas are cut off white the fruit is still green by cutting down the entire bearing tree. The bananas are then shipped to market green and allowed to ripen 'off the tree' because shipping ripe bananas = a lot of fruit loss.

In home banana production most people leave the fruit on the tree until its mostly ripe, cut off the hand, and leave the mama up while she slowly naturally declines and dies back then they remove her.

I don't think you are going to be able to separate the roots. I would just un-pot it and cut the old stump off as cleanly as you can. An old bread knife works well if you don't have a machete. There used to be a banana research station near where we lived and they would just hack off the pups and any attached roots would be cut off before it was replanted. I would not strip off any roots from your pup this time of year, just get rid of the old stump. and add fresh potting medium. Use the largest pot you can find that fits your spot. (maybe tell the spouse to get a smaller vehicle. )

Thank you @gina1960, @christine and @ardesia I was going to use "unapting" to impress my other garden friends with how good I was with terminology. Never once thought anyone else had typos but me. I do have a machete and will get busy with the bananaectomy very soon so baby can grow. I winter over the banana in the garage or simply lay it on the ground and cover it for a light freeze. It works for me. So it's growing slows but never stops. I didn't know about the one and done thing and was surprised when Mamma Banana died back. But thrilled to have the offspring. Thanks, Ladies!

Many tropicals are one and done. Each stalk of heliconia, most gingers (Costus can be an exception, they can produce keikis from spent blooms) only produce one flower per stalk then its all over.

Yes. I suppose I think of bananas as trees. Can you imagine if more trees were one and done? Yikes!

@gina1960, so leaving the stumps won't prohibit new pups from spreading and growing? I have several in my 'banana tree garden' that did nothing last year, so I was just wondering if they needed to be removed.

After my bananas flower, I leave that tree up as long as I can. Basically until it threatens to fall over on it's own. Since they can be heavy I try not to let them fall or they will crush adjacent plants. Then I cut them in half only cart the top
Off to the compost and leave the stump. Leaving the old tree up helps supply energy to new pups. And only cutting it by half does the same. The old stump will eventually turn to mush on its own

I used to cut the trunk into slices with a chain saw and leave them around the base of the plant to compost and provide some free nutrition.