Why does the pronunciation of final consonants change in Korean?

Question

Hello! It's been 8 months since I came to Korea, and I am currently studying Korean in Itaewon. These days, I am practicing Korean by reading K-Pop lyrics, and I have a question.

I saw the word '빛나' in the lyrics, but the final consonant 'ᄎ' sounds more like 'binna' rather than 'ch'. Why does the pronunciation change like this? Does anyone have a similar experience?

I tried looking it up online and asking my Korean friends, and they said that the pronunciation of the final consonant changes depending on the context. However, I am still confused. If anyone can explain this in an easy-to-understand way, I would really appreciate it.

I would be very grateful for any advice on Korean pronunciation!