Your therapist's attitude to adoption is not unusual, sadly. Even therapists come to adoption with their own world views, which are often based on nothing more than watching Long Lost Family. In fact, for a while, anyone providing adoption related therapy to adults had to register with Ofsted - uninformed therapists were doing so much damage (they stopped this in 2024 as it was causing other problems but the underlying issue of uninformed and prejudiced therapists still remains and it still applies to children's therapy).
Anyway, if you want to adopt, social workers look very closely at any potential issues in your background. They would want to be assured thst you would cope with the challenges of parenting a child with kown or unknown issues and that the child wouldn't end up back in care.
This doesn't happen in surrogacy, which is one of the criticisms of surrogacy and also one of the reasons some people prefer it over adoption.
Previous setbacks are not an absolute barrier to adoption - you can actually use them and how you coped to show how resilient you are. But equally you do have to be realistic about whether you would in fact be triggered.
I adopted two girls supposedly without significant issues but tbh, before children start school, it is easy for social services to make out everything is fine. If it's not documented, they won't mention it. And the children are with foster carers, whose priority is keeping them fed and safe - they are not necessarily taking them to play groups or parties, where their differences/difficulties might be more obvious.
My biggest concern for you would be impact on your existing child. Jealousy perhaps. Your life can start to shrink as you can only do the things your adopted child can cope with. You may find they can't cope in childcare and you give up work. Other families won't do play dates. Family and neighbours get angry and start avoiding you. Teachers are infuriated with you. Clubs are increasingly unwelcoming. You end up massively isolated. This is what happened to me and it is whst happened to many if not most of the adopters I know. I didn't have a birth child in the mix or any big previous issues and I coped. I am proud of what I did and of how well my girls have done.
But it's a huge undertaking. I think it is very hard work and not for everyone and not just a way to create a family through Plan B. You have to start from the premise that you are offering a chance to a traumatised child. They generally need so much additional support. Imo a lot of adopters who run into problems do so because they tried to parent like the child was similar to a birth child and don't spot the early signs - and even somebof those who do everything they can, still run into severe difficulties because you cannot treat things like foetal alcohol syndrome or the ongoing effects of developmental trauma, drug withdrawal etc.
Lots to think about.