Q.repotting and pruning plant
Should I repot and prune the tallest stem since it is leafless in the center? I have had this plant indoors for approximately 18 years, and since moving to a house without a high two-story foyer with overhead windows 3 years ago, the plant has become sparce in the middle of the main trunk, and now I’m noticing the lower newer trunks have started to drop leaves and the trunk branch is darker in parts of the trunk. Is this root rot? If so, can I repot using the same container after a bleach washing? I live in zone 5a, in Indiana. Should I wait to repot until spring as long as I lighten up the watering amounts? I would like to propagate and start a new plant with this and didn’t know if I should consider cutting the tallest stalk in the middle just above the leaves, removing the big bare middle from this tree. I hope the pictures will help make sense of what I’m asking. Thanks!
Sincerely,
Mary Clore

The most common problem with Schefflera is overwatering which will cause root rot.
Check the soil before watering.
You certainly can reuse a pot and washing it is a good idea. If you repot always use fresh good quality potting soil.
Here are links with more information.
https://www.gardeningknowhow.com/houseplants/schefflera/schefflera-plant-care.htm
https://www.gardeningknowhow.com/houseplants/schefflera/schefflera-plant-cuttings.htm