Hello! I have been dealing with a trimalleolar ankle fracture since April 25 so I can understand a bit of what you're going though. I actually broke my ankle 6 weeks into my 12 week maternity leave, so I had to be back 6 weeks post injury or risk not getting my job back! I work in the ER and fortunately my employer was able to work out allowing me to do triage with a tech to help out with vitals/rooming patients etc. while I was still non weightbearing. I spent about 2 weeks non weightbearing at work and am now doing a gradual return to full duty. I am currently allowed 8 hours per shift of full weightbearing in a cam boot. I am currently 8 weeks post-op.
In regards to your question, it is my understanding that the ADA does not apply to temporary disabilities and your employer is only required to provide accommodations for your temporary disability if it is related to an on-the-job injury. I'm not 100% versed in this topic though so I may not be entirely correct. I really hope you are able to work something out with your employer to allow you to go back to work! Unfortunately I don't think they are required to accommodate this injury unless you sustained it at work. I would try and get ahold of the job description for any of the positions that you are attempting to transition to and see what they say specifically about walking/lifting/standing etc., as that is probably the determination that your employer is going off of to say that these jobs would not fit within the guidelines of your work restrictions.
*Edit to add: I now see this post is from March so hopefully you have figured out a solution to your problem by now!