See this:
https://www.reddit.com/r/8bitdo/comments/7yhs25/8bitdo_controllers_work_fine_with_wii_wiiu/e3ensia/
text:
A small update on this: 1st august 2018.
Hi, essentially 8bitdo has moved on to new products, and is not considering investing on the wii / wii u scene, as worthy of their time.
As it has been said, their FW is often buggy, and despite lack of a great 3d party wireless controller for the wii /wii u their controllers never took off.
Their current offering is aimed at adult money-investing retrogamers and "heavy" investors in console paraphernalia, not console users searching for RELIABLE controllers.
The use of xinput - BT / RetroReceivers should have been the holy grail combination for cross platform use of controllers, but....Buggy firmware, complicated and subpar connectivity have made those controllers a novelty gamer item rather than a new norm to aim for.
Then there is the issue with all nintendo products: CHEAPNESS.
Nintendo does not want to pay royalties or rights full stop. So no DVD or Blu-ray movie ability, AND no Xinput / USB controller connectivity.
Instead they go for the OLD FREE TO USE (as long as you do not request IPs) i2c protocol that they use for the wii, wii u, NES & SNES minis.
They also do not share tech so retro engineering is needed and it is a WAAAAAAASSSSTE of man-hours.
So 8bitdo tried it, then said ok now let's just make some money out of this. That is why you get even on the switch, buggy FW, and ZERO support.
The solution that works BEST for a wii U, is to use the RR to connect the 8bitdo controller.
Either as a wii classic controller, OR do this:
CFW your wii u.
Then set up your 8bitdo controller to work with your RetroReceiver as a XINPUT device.
Then use a usb cable to link your 8bitdo RR to the wii u.
Use the hid to vpad homebrew to map the RR / 8bitdo controller (logically seen as a wired Xinput controller) as a wii u pro controller.
And here you are, you can play Zelda BOTW with an 8bitdo controller wirelessly on the wii u.
Seek details on relevant sites. Duck duck go is your friend...