Welcome to this forum. Your first post is one of the best that I've seen. It is intelligent, articulate and relevant to the topics discussed here. First, let me congratulate you on getting back into cycling and losing a significant amount of weight. Your current bike is perfectly fine for all around riding for health, fitness and transportation. As far as your original question regarding fixed gear bicycles, rather than go into an extended dissertation, I'd like you to first read the following article by the late great Sheldon Brown who is the great guru of fixed gear bicycles.
https://www.sheldonbrown.com/fixed.html
Once you have read this, please feel free to post any further questions that you may have on this topic. One thing I would say is that you should not ride a bike on public roads without brakes. It certainly can be done, but it is very risky, especially as we get older.
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