Stay or go. That is your first decision.

If you stay: After 3 months you should have a good feel for the project. After 6 months you should be able to regularly make small contributions.

After 9 months: Spend 10% of your time documenting the problems you see and the changes that might solve those problems. Spend 10% of your time planning another work project that is unrelated to the main project. Spend 20% of your time honing a skill you want to learn. Spend the remaining 60% doing the work you were hired for.

After a year, if you feel the same way, discuss with mgmt + senior the problems you’ve been documenting and if the changes you suggest are something that should be implemented.

Iterate.