GPUI development predates Sequoia's funding by about two years.

Companies start with founders funding themselves through savings and friends and family rounds before institutional investors are usually even interested. But make no mistake, they start it as a commercial venture, otherwise they wouldn't have taken VC in the first place, nevermind that VCs wouldn't have funded it if not for their pitch on how it could become a billion dollar company.

And since Sequoia? It is primarily the Zed team working full time on it, which costs money.

IMGUI and other GPU accelerated toolkits exist and have been created without billons of VC revenue.

In fact the entire Qt group is just work 650m EUR

Who said anything about billions? I just said that it costs money to pay people to work on OSS, which is accurate as ImGui is sponsored by companies and Qt is a commercial entity with infamous licensing. VC doesn't necessarily mean billions in funding.