Same as before, OP is free to what she wants. She is perfectly entitled to end a relationship and have an unprotected one-night stand with whoever she wants at any point. The Covid thing probably makes this illegal at the moment, but few people seem to be bothered about this.
She can do what she wants. When you come on MN a and ask for opinions about what you’ve been up to, you will get a range of views. People speak about there not being room for judgement, but when you ask for comments on things you’ve done,of course you will get them and not everyone will say ‘yes great, what you did was perfect’
There’s often a difference between what you CAN do and what might be the best course of action in many circumstances. I really don’t think it is true to say that in all situations, all options are equally good and they are all neutral and just a matter of choice. As others say, many have made choices like the OP did at some point in their life and others might have never done that. All of us at some point in our lives have made choices which we were free to make, but which we ourselves perhaps look back on and wish we hadn’t, or maybe we don’t have that feeling of regret at all, but others wouldn’t think the choice we chose was best.
Overall, OP made a choice and did something some people on MN would have done and something lots wouldn’t have. Most people agree it was her choice to do what she wanted. She did ask for opinions though....and I don’t think you can ask and then only accept or be willing to tolerate answers which say you did the right thing. And that goes too for others who join the thread....there isn’t just one view and AIBU is a discussion and nearly always prompts a range of views.
My personal view is that OP is in a hard place at the moment and pretty vulnerable. Her relationship break up has been really difficult for her and she has been living with her brother and not in her own home and she’s a bit all over the place. I have huge sympathy. Of course she was feee to have sex with whoever she wanted in this period, but her choices have complicated what is already a tricky situation for her. That doesn’t mean she had no right to do it or her brother had any right to tell her she shouldn’t have, but at the same time, many will wonder if things like this are a big help for her current circumstances and attempts to get back on an even keel. Context does remain important. Choices that in some contexts would seem fine and simply a matter of choice without much consequence, can be very different in an altered context. The context here is one of being vulnerable having just come out of a relationship and also being in a pandemic. Context is so important.