I use All The Mods 6 pack with some additional mods, but I dont use sodium, optifine etc.

Please make sure the forgeLightPipelineEnabled and experimentalForgeLightPipelineEnabled settings in the forge-client.toml config file are set to true.
If the problem persists with these settings, then I need you to provide the specific versions of Forge and FramedBlocks (a forced crashreport on pastebin.com or gist.github.com would be useful as well).

It.. partially worked. Now shadows on light gray parts (framed prism corner) look weird.

That's a known issue that I am currently looking into but haven't found the root cause yet.

Found the problem, will be fixed in the next release.