Hey I totally get where you're coming from.
You even making this post is absolutely amazing, you are acknowledging what you are feeling which is one step closer to your goals, you should be so proud. I'm currently in year 11/12 and have been struggling with studying and being motivated for anything and 100% feel like i'm letting myself and others down - it's very common, especially in teens.
Even the fact that we came out of lockdown makes it so much harder, you are not alone. I know talking to people can be hard, expressing your feelings to someone else with the thoughts of what the other person will think of you but trust me, it immediately makes you feel SO much better. Sometimes when I don't feel like talking to someone about how i'm feeling, I just have a shower and talk to myself and honestly, it works wonders but it doesn't amount to hearing someone else understanding.
Again, there is nothing more convenient in lockdown than to sit on your phone on tiktok and things, It takes up most of my day. It's honestly parental instinct to draw being on your phone to being lazy, but I'm assuming they want the best of you and that it's coming from a good place. I too feel bad when I just sit on screens instead of studying and thats a sign, use it to shut them of, lock them up if you have to and do it, use all of your will power.