My advice to learning test automation in this form is: don't

Look up the testing trophy, try to do everything using any tool but Selenium until you absolutely have to. You'll notice that you can come very far using integration tests, you'll also notice the tests are fast and reliable. Something selenium tests rarely are.

For frontend, look at testing-library or storybook with test runners. Former is more lightweight but a hassle to debug, latter is heavier but much more visual and easy to maintain. Both are not flaky and fast and easy to run in a ci pipeline.

Run your tests as close as possible to the logic, you'll get the quickest feedback.

Once you're done with all this, make a happy flow E2E test or two. And I'd use typescript instead of Java. Then you have some hope of a frontend dev wanting to help you maintain it. And playwright instead of selenium, simply more modern and thought out