The constructor mymodel = Chain(layer1, layer2, ...) takes multiple arguments. Calling that model mymodel(x) takes just one. I’m not sure what model_weights and model_univ are meant to be in tbnn_opt because you generally wouldn’t separate model structure from weights in Flux, so this seems like a better question for one of the SciML help channels.
This also seems like something specific to only SciML and should likewise be asked there 