Process modeling tools provide enterprises with the ability to model, implement and execute those models. Process modeling tools help enterprises gain an overview of their processes.
Process modeling tools enable enterprises to:
design and analyze business processes and architectures
analyze the cost-effectiveness of processes
https://aimultiple.com/process-modeling-software
The famous Process modeling software is Lucidchart, while Visio is also good for a simple processes. Nowadays Microsoft and Visio are available everywhere, so you can use them.
It depends on which process do you want to model and the level of detail that you want to model them with.
If you want to construct the models while having large control over them, there are available options like R studio or Python. If the control is not the most important, but still your model is related to the process data analytics, you may want to use RapidMiner.
An available alternative for a modular/unit operation process simulation approach could be DWsim, which is an open-source, CAPE-OPEN compliant chemical process simulator.
DWSIM (https://dwsim.inforside.com.br/new/) is a free simulator for modeling chemical processes at the flowsheet level (similar to Aspen or Unisim Design).
MS Visio is not free anymore - it has been removed from most Academic packages (at least in Europe: you may be able to run the application, but no built in model template are accessible now). Seem to be the same with 365 (and I am not aware of free online access).