The keywords MIPI and DSI are a trap, and I must admit that I fell for it as well in the past.
The DSI (Display Serial Interface) is a specification from the MIPI (Mobile Industry Processor Interface) that soley describe that for communication between controller and display a serial bus is used, the electrical specifications and how the communication protocol (package size, checksums, error correction, …) works.
Unfortunatley it does not include a connector definition, nor does it give recommendations about the order of pins. As far as I understand one is not even required to use those FFC (Flexible flat cable) connectors. Mainly because different sized displays can use different amount of DSI channels. So every display producer is free to choose the pin layout and so they do. Essentially a simple 20-30pin connector for LVDS/RGB on the board would have been probably more usefull.
If you do not want to use the HDMI connector and you need higher resolution, you could try to get hands on an interface bridge like DSI to DPI(RGB) or DSI to LVDS. Pairing this then for example with parallel RGB or serial LVDS screens instead. But it requires you to build your own specific bridge board/hat/friend.
However, for the driver you would need to try to integrate this kernel patch for the TC358764, to get support for the DSI to LVDS bridge. Which should show up in the kernel configuration next to NXP and Parade eDP/LVDS bridge.
If you can live with lower resolutions (max ~800x480) you can also try to go the SPI route. This is what I am currently follow as I only need 480x320. Those screens are controlled via the GPIO pins for serial SPI/I2C. I saw some advertisements for rather expensive1024x600 screens, but not sure they work, as the pictures usually show them with an HDMI connection.