https://www.emtbforums.com/threads/whats-the-consensus-best-diy-frame-right-now.30884/

https://www.emtbforums.com/threads/dengfu-e55-and-e56%EF%BC%8Cnew-selection-of-diy-frame.31400/

If you want a Brose, Bosch or Shimano motor your best bet is to buy the cheapest model that meets your needs and swap out the components you don't like.

I'm not aware of any Western brands doing it so you'll likely have to look to China for a frame. Most appear to be built to take bafang motors.

eg. https://www.aliexpress.com/item/1005004855977156.html

Emtbforums.com has a DIY forum. Lots use Dengfu frames, Bafang motors, although some of the Chinese frames will take Shimano if you prefer.

If they are, it’s normally from shops that have split bikes, rather than official release

Not even remotely in budget, but just in case useful I know that Pole and Nicolai do frame only (motor, shock etc + whatever else you need) options for the Voima and E-Boxx respectively.

There's this

And is there anything on Chinertown?

Checking out the Facebook groups, bit scared of the self build import route as whilst I’m squared away with the mechanics the electronics side of things is a bit daunting.

I’ll have a look at the emtb forums and see what there, but frustrated as have a box of build kit for a frame that I was really looking forward to using however they’re on pause and given the way things are progressing may never see the light of day.