Trading loss relief – income tax

I am really trying to understand how trading losses are relief against income better. I have a scenario:

A earns in 2023/24 £90,000 annual PAYE income and pay taxes directly through employer
However, A also traded options in 2023/24 and lost all invested £42,000.

My questions are;
1. Can A claim tax relief on the full £42k options loss against the £90k income in 2023/24?
2. If yes to the above, is this done through self assessment?

Scenario two:

Assuming same case as above but the loss was made in 2020/21. Can A still go back and claim the relief against the 2020/21 income, eventhough it is currently 2024?

I hope someone can help with the above query.

Thanks,