You may wish to look through Products and sites to practice testing on if you haven’t already.
Is it something you do within your team to help train them, give them a better understanding of testing, stop them from going rusty depending on the type of work they do, etc?
It also feels like you are manually performing mutation testing, changing your source and seeing if their tests are picking up the changes. If it isn’t something you have looked into (it’s still quite unknown/niche), have a look into it.