i think thats a very difficult question to ask as there will be differences in every single school in the UK. The grade boundaries this years are meant to be returning to 'normal' so they should be comparable to the 2019 grade boundaries used before COVD. Exams won't necessarily be made any easier for this year, they are meant to be standard. When looking at the 2019 or any other boundaries i would say my recommendation would be to add 5% on to each boundary so you are safe when aiming for a particular grade/