After I've updated to source tree 2.5.5 it prompted me:

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SourceTree.exe - This application could not be started.
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This application requires one of the following versions of the .NET Framework:
.NETFramework,Version=v4.7.1

Do you want to install this .NET Framework version now?
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Yes No
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However I CAN'T install this .Net FW  version because my Windows 10 version, which is controlled by my company, doesn't support this FW version.

Version 4.6.2 is the last supported by this windows 10 Build 1478.

https://docs.microsoft.com/en-us/dotnet/framework/get-started/system-requirements

 Please, roll back the support for .Net 4.6.2 OR prompt-me to install a new dotnet version BEFORE upgrading source tree version, it's in an unusable state