Congrats on your Discover graduation . . . I too started with a Discover secured card that graduated to unsecured -and- now my CL is $5.6k -but- no CLI since January 2021. I'm still very happy!!!
A soft credit hack I use it to apply for a Discover personal loan, when you know they will say no. They tell you right away why, you get to see your updated FICO score that doesn't show up for months on the Discover app.
See if you can get approved for another Discover card, ask for CLI's every 31 days maybe? I went from $8700 on my first Disco to $20200 on it now. Took years for all those CLIs. It can be done tho. I had a repo active on my score till last month.
You can do it!
Congratulations on your Discover graduation and CLI!