So I stayed at home instead.

So, earlier, I promised several of my students that I would record such anthis audio for them.

The second thing is that I creatfilmed a video of the 4th and the last plant I bought for this Chinese New Year.

I had planned to visit an ancient building today, but it has been raining heavily since this morning, so I stayed home instead.

So I {stayed | have stayed | am staying} at home instead.

We generally try to avoid beginning a sentence with “so”. It’s more natural to merge this with the previous sentence.

I created an audio (recording) for my elderly ladies' yoga class.

“Audio recording” sounds more natural to me.

An alternative:
I recorded some audio for my…

For some people, it's more difficult to fall asleep as they get older.

Alternative: Some people have trouble falling asleep as they get older.

So, earlier / previously, I promised several of my students that I would {record such an audio | make an audio recording like that} for them.

“Such an X” sounds very formal.

I have already sent it to the class (after finishing it).

“After finishing it” could be omitted since it’s implied that you finished it before you sent it.

The fun part is that I used an AI to read the text I wrote and then used my voice tone to overlay it -- the AI even imitated my southern accent.

You can watch it (listen to it?) here: https://www.youtube.com/watch?v=k8Bu4UYCzkA

“Watch” seems strange for an audio recording.

If you are currently learning Chinese, you can also use it as (your) relaxation audio before sleep.

The second thing is that I created a video of the 4th and the last plant I bought for this Chinese New Year.