Thanks for your question.

I am having a slight problem in identifying this house plant, but I think it is a type of wax plant. It also has common names of honey plant and porcelain flower. Its botanical name is Hoya carnosa. If my identification is correct, it is a relatively low maintenance household plant. If not given sufficient light, its leaves will yellow. Perchance have you changed the location of the plant within the last year or so? See the following for more information about this plant:

https://en.wikipedia.org/wiki/Hoya_carnosa

https://www.planetnatural.com/hoya-carnosa/

https://www.guide-to-houseplants.com/wax-plant.html

Other than a change in location, the leaf yellowing might be due to other things.

1). Too much water can lead to root rot, which in turn can cause the leaves to yellow and drop. Make sure the plant is not sitting in water and allow the top inch or two of the soil to dry out between waterings. You may want to consider repotting the plant in a larger pot. If you do this, carefully inspect the roots to be sure that they are firm and not soft. A new pot must have drain holes at the bottom.

2). Underwatering can also cause yellowing leaves. Check the soil moisture regularly and ensure that you water the plant only when the top inch of soil feels dry. As it turns Hoya plants are somewhat drought-tolerant, so it's better to underwater than overwater.

3). Yellowing leaves can also be a sign of nutrient deficiencies, particularly if the older leaves are affected first. These would be the lower leaves of the plant, which seems to be the case as seen in the pictures. Hoya carnosa usually benefits from a balanced liquid fertilizer during the growing season (spring and summer). Follow the recommended dosage on the fertilizer label.

4). Hoya carnosa prefers bright, indirect light. If it's not getting enough light, the leaves may yellow. As I asked before, have you recently changed the location of the plant?

5). Hoya carnosa prefers consistent indoor temperatures between 60-80°F and humidity levels around 40-60%. To the extent possible, your plant should be in a location that satisfies these conditions.

6). It's normal for older leaves to turn yellow and drop off as the plant matures. This is part of the natural growth process and as long as new growth is healthy, it's not a cause for concern.

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