I'm following the steps here in order to use all my computing power (10-core Intel i9 CPU) and solve a one-instance abstract Pyomo model. However, it seems that the solver is just using one CPU core and it takes more than 2 days to return a solution for a 50-node input (with 10 nodes it just takes seconds.) any help about making Pyomo model run in all available CPU cores?
Depends on the solver and the model. Some solvers are single threaded others operate in parallel. Typically, MIP models can benefit a lot from parallel processing. LPs not as much (some interior point methods do a reasonable job). Beware that you need a ton of memory to allow the solver to run the model in parallel on many cores.