There are very serious companies making investment in fission.
The problem is that there are very few places in the West where there is anything like a market.
In the US, any progress is basically blocked because the only type of reactor that can get a license is a PWR. Anything else is essentially impossible because of incredibly dumb and regressive technology depended licensing schemes. Thankfully even the DoE has realized this and his slowly changing course. However we are talking decades.
NuScale is building a small PWR, that is why they were able to do it in the US.
That is why, most Western advanced fission companies go to Canada. Canada has a good internationally reorganized regulator and a regulatory framework that is sensible.
See their process here, and a list of companies going threw the process:
https://nuclearsafety.gc.ca/eng/reactors/power-plants/pre-li...
As you can see Terrestrial Energy Inc. has passed into Phase 2 in 2018 and is thus the furthest along company in terms of bringing a GenIV plant into commercial operation.
What we need to realize is that these companies operate with comparatively little money and thus are operating pretty slowly. If a government would to really push these projects, they could be much faster.
That said, France of course had GenIV plant operating and producing as far back as 1986 but sadly the project was killed by short sited politics.
There is also an interesting US company called Kairos Power. They are attempting to go threw licensing in the US but they have a very complex plan to 'hack' the traditional path of licensing.
My personal favorite design is by Moltex Energy as it is a molten salt reactor that is burning nuclear 'waste'.