Hi!
I can't seem to find any notice about what version of UCSI is supported on TPS65988DH device. It's not stated in the data sheet or the Technical Reference Manual.
Also, according to chapter 4.15 in slvubh2b.pdf (Technical Reference Manual) some data descriptions do not match the UCSI specification. For example, Table 4-52. UCSI - PPM_RESET, byte 3, bits 6:0 "Connection Number". According to UCSI specification (versions 1.0, 1.2, 2.0 and 3.0), bytes 3-8 of PPM_RESET is "Reserved and shall be set to zero.". So custom ucsi frameworks (such as the one in the linux kernel) will most probably insert zeros in bytes 3-8, which will result in "Task Rejected" according to "Connection Number" description in Table 4-52.
See linux implementation of PPM_RESET here: https://elixir.bootlin.com/linux/v5.19.17/source/drivers/usb/typec/ucsi/ucsi.c#L870
Best Regards,
Mattias