Autocomplete does not work with DxCore (and some megaTinyCore boards) in Arduino IDE 2.3.2 on 64-bit Linux

[ETG153]

As it says in the title, attempting to autocomplete (ctrl-space) anything will have all options grayed out and crossed over.
Does not occur when using any other Board library, such as stock or esp32.
Also occurs on some megaTinyCore boards, such as ATtiny3226/3216/... and ATtiny3224/1624/... but not with ATtiny3227/3217/... or 'Official Microchip Board'

To replicate:
Install Arduino IDE (tested with v2.3.2)
Install DxCore through the boards manager (tested with 1.5.10 and .11)
Create a new sketch or open an existing one
Set Board to be anything from the DxCore library - All series with or without Optiboot exhibit this behavior
Attempt to autocomplete anything
All options in the autocomplete window should be crossed over with a line and grayed out, unlike normal operation where they should be all available

System info:
OS: Linux Mint bookworm/sid (virginia) x86_64
Kernel veersion: 6.5.0-45-generic

Has not been tested with Windows, Mac, or 32-bit Linux

[SpenceKonde]

I've heard this before - does anyone have any information on this and how to support i?

[wke67]

This problem has same root cause as issue #471 'Hover not working in Arduino-IDE'. The problem is with the Arduino Language Server which relies on clangd to provide the hover, autocompletion, code checking functionality. Arduino-IDE (2.3.6) ships with clangd 14. This version does not know about newer AVR chips like the AVR64DD28. I have replaced clangd and clang-format with the up-to-date version 21 downloaded from https://clang.llvm.org/ and replaced the old version in the 'Arduino-IDE/Resources/app/lib/backend/resources' folder (Debian Linux, Arduino-IDE downloaded as zip). Problem solved!