If you've seen an increase in negative behaviors since the beginning of the pandemic, you are not alone.
The uncertainty and change in routine have been difficult for many families, especially for children, as they don't know how to deal with all the changes happening around them appropriately.
Kids thrive on routines as those routines allow them to feel safe and in control while understanding the world around them. When patterns are altered and keep are continually adjusted, they often don't know how to process them.
Children act up because they're feeling overwhelmed, worried, scared, sad, frustrated, stressed, etc. Understanding why they may act up allows parents to address better the root cause of what is causing their problematic behavior.
If you understand that they're acting up because they're feeling overwhelmed, you can create daily opportunities for them to meditate or take a break. If online school is causing them frustration or stress, you can implement procedures to reduce those feelings. If they're sad because they're not seeing friends or missing out on things they love, you could create online or different opportunities for them.
The skill of Following Instructions helps a child to feel in control because they understand what is expected of them. Following Instructions is can be used with children of all ages--including teenagers. 
Following Instructions is one of the first behavior skills we recommend parents teach because it provides such a framework for all the other behavior skills.
Following Instructions provides the following benefits for children.
It allows children to know precisely what they are supposed to do, which reduces stress and frustration. 
It meets your child at their level by enabling parents to break down complex instructions into small steps.
It gives your child confidence that they can accomplish tasks.
It allows you to focus on the good things your child is doing, ie completing a job, which shifts negative behavior sooner.
You can find the behavior skill of Following Instructions at Smarterparenting.com