8 pullups is great. To get to high rep counts you need more overall weekly volume. One thing you can do is don’t think just about how many you can do in 1 session, but instead per day or week. For example, when I was specializing to get to 20 in a row, my preparation would simply be 5-6 sets of 10+ reps, but the progressive overload is that the total for the day’s work started at 60, then I would add 5 reps to the total quota for the next week’s working sets. That achieves the “progressive overload” requirement to stimulate growth. It is MUCH easier to add 5 reps at some point in the day than to add 5 reps right after the end of the last set. The progression is stronger if you cluster your work together, but if you can’t progress in clusters, then you space it out until you can progress. Eventually around 85 reps per day, the 20 in a row became feasible. So by this point most of my sets were 14-17 reps.

This is similar to how you progress in body building or strength training, at an advanced level you can’t progress every workout, so you may add an extra work day elsewhere in the week. Or you just add an extra set to one of those days, the spacing gives you more window for progressive overload and thus progress over 2 weeks or cycles instead of every week. The growth isn’t as rapid when spaced, but growth will still happen.

Also if you aren’t lean, get lean. Pullup reps scale very strongly with weight loss, so if you’re packing excess bodyfat, your reps will be pretty significantly depressed.