I was taughtlearned how to painting today.

Or alternatively: "I took a painting class"
"I was taught painting today" is in the passive voice and leaves a lot of questions: who taught you? Where were you taught?

Recently, I'mI'm still not better able tot painting than I was before.

Finally, I was scolded by teacher.

"Finally" makes more sense in the context of you giving an explanations of a variety of things that happened. Since that didn't precede this sentence, I just removed the word altogether.

Sad Day

I was being taught painting today.

"I was learning about painting today." would sound the most natural, but adding "being" is ok. Saying "I was taught X" implies you learned X completely. "I was being taught X" means you are learning about X.

Recently, I'mve not better able to paint than beforeen getting better.

Or "Recently, I haven't been improving"

Finally, I was scolded by the teacher.

I'mt made me sad, but I should practice more and more.

I was taught a painting today/ I was taught how to make a painting today/ I was taught how to paint something today.

Other ways of saying it more naturally too!

Recently, I'm not better able to paint thanas well as before.

"as well as" is common in english

FinallyIn the end, I was scolded by teacher.

I was taught painting today.

I went to art class today.

Recently, I'm not better able to paint than before.

Recently, I haven't improved in skill.

Finally, I was scolded by teacher.

I ended up being scolded by the teacher.

I'm sad, but I should practice more and more.

Your sentence was fine, but this feels a bit more natural for this situation.