Starting with QGIS 3.12.0 & MDAL 4.0 (unless the milestones get changed completely), the ESRI TIN files (ADF format) will be supported through the MDAL driver.
MDAL GitHub ReadMe:
Esri TIN: Format for storing elevation data as a triangulated
MDAL Pull Request: Add support for reading arcinfo adf tin layers #162 #164:
First Draft, the mesh seems to be loaded. Need tests to verify if the geometry is ok.
QGIS Issue: Support for 3d visualisation of ESRI TINs #32240:
QGIS is going to support reading of ESRI TIN files as a mesh (through
MDAL) with this PR: lutraconsulting/MDAL#164 It would be great to have
support for 3d visualisation of the data too. QGIS 3D already supports
visualisation of 2dm files...
QGIS Pull Request: [Feature][Mesh][3D] new 3D mesh layer renderer #33837:
This PR change the 3D mesh renderer approach The new approach is based
on OpenGL shader. By this way, the GPU handles rendering wireframe and
color ramp shading.
There are two entries to render the mesh layer in the 3D view : choose
the mesh as terrain in the config widget activate the 3D view in the
layer properties. The user can choose those settings enable/disable
smooth triangles enable/disable wireframe choose the line width and
the line color of the wireframe change the verticale scale choose the
style of the rendering : unique color or color ramp shading settings
the color ramp shading as for raster layer For now, the mesh can be
rendered as a TIN but rendering dataset is not supported. However the
infrastructure is adapted for a future PR.