I find Go pretty boring and lacking, the only new concept there is the green threads. Python is very practical but also boring. I recommend Rust, as it has new interesting concepts not found elsewhere. Considering your background, I'd also recommend F#. It's fun, interesting and offers new insights for a developer coming out of procedural or OOP. The added benefit: you would be able to add it to your toolbox as a .NET developer.
I considered f#, but never really got enthused about it. If I were to go the functional route I'd probably do elixer or erlang. It sounds weird but I find the syntax intriguing
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