How to properly apologize to an online friend?

I had finals and make-up exams and I've been dealing with them for like more than 3 weeks. University made me really depressed and stressed, I had hard time with communicating with my friends. I still talk to my boyfriend, my dad and some of my really close irl friends regularly but I have hard time continuing that with my other friends. I'm not proud of this, I'm really introvert and communication was always hard for me.

Because of uni I haven't been able to talk to my online friend regularly. It's been more than 2 weeks since I havent responded to her message 🥲

She's been my friend since 2023, she's from another country and we shared many interests, she's a dear friend of mine and I want to properly apologize to her. I feel so ashamed, I don't know what can I say to her.

I really appreciate help 🙏