I wouldn't call this minimalist ambient, there's a fair bit of instrumentation, structure, and a whole chord progression. There's very little texture, the piano feels to natural and thin with seemingly no FX or dynamics, it playing over a chord changing synth-style pad doesn't quite feel full and fleshed out either.
I think limiting yourself to stock plugins in something minimal like bandlab hurts your production quality, especially when you're mixing on laptop speakers. There's absolutely no low end to this track, or mid-low. These's an entire lack of sub-high frequencies that make the whole track feel incredibly thin. Like it's 4 minutes of of a motif and nothing much else to carry it.
It's not a bad track at all, it just doesn't feel like it's really finished or had much thought put into it. Embracing creative limitations doesn't mean you have to drop a hammer on your foot. You can use stock plugins but use them creatively, but something like bandlab that isn't offering you high quality stock plugins for something like ambient feels like the wrong challenge to tackle in an ambience jam.
Either way, good work.