After updating to version 1.3.8 Neoforge, every block gains a lot of hardness, and now it is kind of impossible to break a block

Uh, there is no NeoForge build of Chisel ?

Had the same problem, just go back a version from Chisel 1.3.8 to the 1.3.7 version. This is a Chisel Chipped Integration issue but I don't know who is the mod author or where to go for their bug reports because they just link to here. I am going to try to find where to report. Am trying here if you also want to report it. https://legacy.curseforge.com/minecraft/mc-mods/chisel-chipped-integration/issues

Uh, there is no NeoForge build of Chisel ?

The link on their page leads here, and I thought it was you

Yeah, that author is just outright lying about the Source link - they should be linking a source to their fork, not this.

For sure. They had me hunting down where they were for and what was causing the issue for two hours. Even on their issues tab they seemed to have deleted any paper trail of issues with their mod too so when looking for issues there just were none there being reported or rather they might have removed it. Keep on keeping on Chisel-Team! Hopefully we can get to the mod author somehow.