Do you support Orange/Banana/Mango/Rock Pi or other Pi lookalikes?

Not the ARM-based ones, no.  TLXOS SFF supports some x86-based Pi lookalikes (e.g. we own an Aeon Up Board and a Rock Pi X), although there may be a few support deficits (e.g. analog audio doesn't work yet on Rock Pi X).

ARM-based products lack the common standards that x86-based PCs have (e.g. for bootloaders and bus technologies), so it's very difficult to create a generic O/S with a fully automated install process that will run on a range of hardware and also has the aggressive graphics optimization that is necessary for thin clients (especially those with relatively slow CPUs).  In practice we'd more-or-less have to maintain a separate TLXOS Edition for each such hardware product.

Moreover, at present commercial software that may be critical for your use case, e.g. Citrix Workspace App or VMware Horizon Client, typically does not support H.264 hardware decoding any ARM platform other than the Raspberry Pi, so any such software will run suboptimally on Pi clones, if at all.

Another problem is that 64-bit ARM kernels lack a compression stub (in the mainline Linux kernel, at least), and have a larger disk footprint than 32-bit kernels in any case, and that we simply cannot fit the 64-bit kernel required by many Pi clones in the space provided for the /boot filesystem by TLXOS 4.x.  We can't make this bigger without breaking backward compatibility and forcing customers to reinstall rather than upgrade.  We'll try to address that problem in TLXOS 5.x.

We hope that ARM platforms will become better standardized in future, e.g. adopt UEFI booting, and that commercial software providers (Citrix, VMware etc) will start providing 64-bit ARM Linux (aarch64) ports of their client software with more flexible hardware decoding arrangements; at present they provide only 32-bit ARM Linux (ARMHF) ports, which means that we have to keep providing a 32-bit ARM userspace even on 64-bit capable ARM platforms (which includes the Pi 4, by the way).

We're starting to look at some alternatives, specifically RK3399-based boards like the Rock Pi 4, but it's still early days, and although we have TLXOS 5.0.0pre running on one of these, at present it performs poorly due to lack of a fully optimized graphics stack.