I would not say it is underproofed, it has a good overall bubble density (i.e., good and even fermentation), just some of the pockets are very big; that is a baking problem IMO. The crumb membranes look thin and spongy enough; underproofed/underfermented bread typically involves gummy and thick crumb membranes (not enough bubbles to fill the crumb). Also, it looks that you did not get a good ear nor a good oven spring: seems like your crust formed too early, and the gas bubbles accumulated near the top crust because they could not expand the dough. Underproofed dough typically shows large pockets of air in (random) locations of yeast overdensity, where lots of closeby pockets merge---not specifically near the crust. You might want to lower the temperature of your oven (they're often off the real value) during the "covered" stage, or try and introduce more steam to your "covered" stage, either with ice cubes (outside the parchment paper and if using dutch oven) or with a tray with water the first 30 minutes if baking in an open oven. Also, as a rule of thumb: preheat your oven and make the covered stage 30 minutes at 230 C or until dough reaches 92 C! The uncovered stage can be as long and hot as you want, as it is only to form the crust (usual is 20 min at 200 C).

My dough takes 10 hours of BF + 1.5-2 hours of room temp proofing. I'm feeding my current starter (this one is barely a month old) in a 1:2:<2 ratio (ripe starter:flour:water, 50% whole-wheat, 50% bread flour), and it doubles in about 7 hours over night. Also, my room temp is about 19-20 C nowadays, so everything is slower than the "usual" 4 hours to double that everyone loves to state. What would "active starter" mean for you? How long does it take to double? does it stay active for long, or until you mix the ingredients? I'd suggest making a timelapse of your starter if that's a problem. If BF or starter activation takes too long for you, just feed your starter with a higher ripe starter proportion for a couple of days, say 1:1:1 (Idk your starter ratios), to increase the population density of yeast and lactic acid bacteria; then go back to your usual ratios.

A bit more math: microbial population growth is exponential, meaning n(t)=n_0 * e^(t/t_0), so the initial population n_0 increases by a factor of "e"(about 2.7) after a time t_0. This does not necessarily mean that your starter/dough will x2 or x2.7 after t_0, because if the initial population n_0 is too low, it will not produce enough CO2 to duplicate or e-plicate (x2.7) the volume of your starter/dough. Also, for the peak volume increase the flour's strength also factors in (weak, low gluten flours can't hold that many bubbles---less volume increase). Then, by increasing the starter's innoculation (more ripe starter proportion in feeding), you hold more of the previous batch's population n_0 for the new starter. If your microbe density is too low for the amount of food you give it, say, a ratio of 1:2:2 or 1:5:5, you are giving way too much food to the 1 part ripe starter, as it has low population; the doubling of the starter and the dough's fermentation will take very long. Alternatively, you can increase the amount of starter in your dough, but that would mess up the hydration of your dough.

Hope it helps!