I currently have a new L009UiGS-2HaxD-IN and am running a CAPSMAN manager on it. I connect to a cAP XL ac RBcAPGi-5acD2nD-XL to it and I see it in the Remote CAP section. IP and all. But when I go to the Radio tab, I don't see the interface in the radio. Any idea why?

Set manager property to capsman on the cap in interface settings. Did you install wifi-qcom-ac on the cap?

See https://www.youtube.com/watch?v=37aff6d14Xk and https://www.youtube.com/watch?v=AkBIQxi-VKs

RBcAPGi-5acD2nD-XL is legacy wifi but it can run wave2 drivers.
So you definitely should consider some options:
A- install wave2 drivers on cAP AC XL (wifi-qcom-ac)
B- drop wireless package on L009 but then you will loose local wifi functionality.

Overview page from Mikrotik:
https://help.mikrotik.com/docs/display/ROS/Wireless

I couldn't find the drivers separately on the Mikrotik website. When I read the details about the different updates available, I discovered that 7.14beta9 has the drivers in there. When I installed it, nothing happened. Is it because this CAP is WiFi-4? I hear in the videos that this has to do with Wi-Fi 5 and 6. I have not heard anything about 4.

That option is available since 7.13 so you didn't do a good job searching nor reading.

Download from mikrotik website all packages for ARM for 7.13.3.
https://download.mikrotik.com/routeros/ ... 7.13.3.zip

In there you will find new wave2 driver (wifi-qcom-ac-7.13.3-arm.npk).

But make sure you understand what you are doing because it looks to me you're not.

@holvoetn already gave a good direction, to make it more explicit:
https://help.mikrotik.com/docs/display/ ... i-Overview (where you can read about wifi-qcom-ac which is necessary for the cAP XL ac)
https://help.mikrotik.com/docs/display/ ... iFiCAPsMAN (things you have to take into account, especially when using VLAN)