There is no question that monolithic applications can be developed using agile practices, and these are being developed all the time. Continuous integration (CI) and continuous deployment (CD) could be used, but the question is—do they use agile practices effectively? Let's examine the following points:

When there is a high probability of having stories dependent on each other, and there could be various scenarios, a story would not be taken up until the dependent story is complete.

The build takes more time as the code size increases.

The frequent deployment of a large monolithic application is a difficult task to achieve.

You would have to redeploy the whole application even if you updated a single component.

Redeployment may cause problems to already running components; for example, a job scheduler may change whether components impact it or not.

The risk of redeployment may increase if a single changed component does not work properly or if it needs more fixes.

UI developers always need more redeployment, which is quite risky and time-consuming for large monolithic applications.

https://medium.com/swlh/how-align-scrum-teams-99b907e67edd