Hi and welcome 
I'm sure I remember one parent from a forum years ago who had had MH difficulties when they were younger, and had been sectioned once, and then had been approved to adopt years later, after extensive checks, including extra medical checks involving old medical records and a consultant psychiatrists report etc.
I can't think of anyone I know who has Bipolar specifically, but I do know adopters who have had other mental health difficulties
When prospective adopters have a health condition of any kind, the adoption agency should always be looking at 'how your condition affects you personally, how it is managed, and whether and how it would affect your ability to look after a child. If it would affect you sometimes, do you have the resources, resilience and support to manage this. It should all be based on you personally.
You will have a medical check with your GP, who will send a report to the agency about your fitness to parent. However when prospective parents have health conditions, depending on the condition, they sometimes want a specialist report as well, or a closer look at your medical history at least. So if you've say, seen a psychiatrist or another professional about your condition in the last few years, you may find an agency would also want to hear from them as well as from your GP.
Basically, it shouldn't be an outright barrier, but you should expect very in depth questionning and health checks about your condition (which as I said, should be about how Bipolar affects you specifically, not about Bipolar in other people/generally). If you can show that you are proactive and seek help, this is always a big plus point, for any prospective parent!
I wish you the best of luck