Now you've installed both, a 32 bit java 1.8.0_251 in "c:\program Files(x86)..." and a 64 bit java in "C:\program files\Java\jdk-14.0.1". As the one in "C:\program files (x86)..." is first on your path, that one will get used unless you explicitly set the path. Generally, "Program Fles(x86)" is 32 bit software, "Program files" is 64 bit. Move that one to the top.
So that means there's no newer mapping at the moment. Fine with me, I'll wait a bit to update my mod.
Still, is there a way to get a list of currently available mappings? I've use https://files.minecraftforge.net/maven/de/oceanlabs/mcp/mcp_snapshot/, but that one only lists 1.15 files (I guess because it's a html file that's updated automatically but not when someone publishes a mapping manually) ?
The 1.16.1 modder download comes with a build.gradle that references
mappings channel: 'snapshot', version: '20200514-1.16'
which is quite old and missing a lot of mappings, for example most of the mappings in Screen are gone.
Is there a newer version of the mappings? And if so, how do I find out without asking forum questions?
Same problem here; this is due to optifine. Removing Optifine helps. So does *downgrading* forge.
Forge 14.21.0.2335 with Optifine 1.12_HD_U_C3 works fine for me, forge 14.21.0.2375 and 14.21.0.2381 don't.