I use clangd (actually, ccls language server) with U++ for several years.
I use it from vim. This works very well for me.
Opening of a project takes about 10-15 sec on a 8 core (16 threads) CPU.
Navigation is much better than in TheIDE.
Language server spends ~1-2 sec. recompiling a file on each save operation.
I'd recommend to take a look at tree-sitter, which is an incremental parsing library.
Both, language server and tree-sitter are built into a new version of vim called neovim, which I recommend to use as a reference example.
We can also move this discussion to a U++ forum.