Build doesn't find .NET SDK even though it's installed

ok so I have change to .net 5 because i only used .net 6 because it was downloaded. But I still get an error about .net 5 so where may the problem be now?

/usr/lib/mono/msbuild/Current/bin/Microsoft.Common.CurrentVersion.targets(1193,5): error MSB3644: The reference assemblies for .NETFramework,Version=v5.0.401 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at [/home/travis/build/zaze06/TextGame/Game.csproj]

full log
travis log (

e[0Ke[33;1mInstalling Monoe[0m

[?1he=e[6ne[He[2JMSBuild auto-detection: using msbuild version ‘15.0’ from ‘/usr/lib/mono/msbuild/15.0/bin’

You didn’t disable Mono installation.

works now thx