GloriousEggroll has released another hotfix for GE-Proton, this time to add the missing proton packaged Gecko and Mono.
Release GE-Proton8-9 Released
Hotfix: Apparently yesterdays build was missing the normal proton packaged Gecko and Mono (the file size was significantly smaller than usual). This build fixes that.
Release GE-Proton8-9 Released · GloriousEggroll/proton-ge-custom