The decision to use Salesforce Flows or Apex Triggers can be hard sometimes and it should be because a few mistakes when making this decision can lead to massive amounts of pain down the line. Salesforce prefers that you click as much as possible which means if your automation can be done with a Flow, you should favor that method before you move on to coding an Apex Trigger. After years of building both, I'll tell you that I favor Apex Triggers over Flows in almost all cases. Here are a few exceptios that might help explain things:
If you have to get input from the user in order to further your process and automation: FLOW
If you have to get input from the user and then make a callout to another system: FLOW with an InvokableMethod for the callout
Every other scenario should favor a Trigger and it all comes down to unit tests. Apex triggers require unit tests while Flows don't even require manual testing. When you start working in Salesforce Orgs that have dozens of flows, many of them will be dependent on each other. One will kick off another or change might kick off multiple processes which kicks off multiple flows. One small change to one of the flows and now you have to manually re-test all of the flows. You'll have to keep track of test cases in a spreadsheet to make sure that you re-test each type of action that might end up in a different result. This is incredibly time intensive.
Some could make the argument that smaller orgs would benefit from taking an all "Flow" method regardless of any rules. This might be true and good for your budget at the beginning, but small orgs grow into larger orgs and before you know it you'll have 20 flows and a new flow error e-mail to review every day.
There's also the argument that a developer costs more than an admin so you should get an admin to build you flows. If you want to start off that way and get yourself going, you should definitely take that route, but as you grow you're going to get yourself into development and those flows will require a lot of support. Some of the really error prone and complex ones will be moved to triggers to gain the benefit of unit tests.
Using Triggers with unit tests allows you to set yourself up for the future. Create detailed unit tests the first time and then feel confident that you can make changes and push them to production as long as the unit tests are all passing. Sadly Flows don't offer that yet, but maybe Salesforce will provide Flow tests in the future that accept certain inputs and check to make sure the outputs are correct. A feature like this might change my mind on the Flows vs Triggers debate!