Welcome to the community and to a Quality and Testing role!
Yes, it can be disheartening to be using an internally developed tool while the industry is using well-known open-source tools.
There is a lot of good news here.
First, because there are lots of open-source tools, you can learn them at any time.
- Can you create a side project in Selenium that duplicates what you do in the internal tool? You don't have to run it in any CI/CD pipeline, just ensure it works locally. This allows you to get experience and see the pros and cons of using different tools for the same purpose.
- Trust me, employers want to see the skill of "tool selection" using a "feature benefits comparison" or a "feasibility report."
- Can you write a blog article comparing the features of these different tools? - What did you learn in the process of duplicating tests in multiple tools?
- Are you able to see any performance differences in running the tests using different tools?
- Maybe you can then use this information to report to your manager to see if the team can use a widely known open-source tool if it gets better results!
Second, think about the concepts you are learning on the internal tool.
- Are you learning about code structure? Object-oriented programming?
- POM - the Page Object Model?
- Are you using 3rd party libraries for the asserts or the test runner? We don't know your tech stack, so is it using things like JUnit, Jest/Expect, Mocha/Chai, XUnit? These are well-known and certainly can be added to your resume!
Next, understand that skills are transferable! Anything you can do in one tool can be transferred to another!
I'm sure I can come up with even more reasons and advice, but this gives you a good outlook to start with!