Plutonium separation can be done chemically, while Uranium enrichment is a subtle physical process. However, to produce Plutonium in the first place probably requires enriched Uranium.
In the official narrative, Trinity was a plutonium implosion device. The first wartime bomb used (Little Boy over Hiroshima) was never tested at all. Presumably, this indicates that a U-235 "gun-type" bomb should be in some sense simple and reliable (or the US got extremely lucky).
A non-official explanation is that Little Boy was fake. The book "Death Object" is skeptical of the veracity of the US WW2 nuclear weapons program. https://archive.org/details/8d-0de-2 The alternative explanation seems to come down to a deliberate hoax by the US military (not new in a wartime) using a "photoflash" bomb, which produces blinding light but not a powerful explosion. It turns out that Little Boy fits the general profile of a photoflash bomb. See the diagram here https://planehistoria.com/photoflash-bombs/ and the later model pictured here https://en.wikipedia.org/wiki/Little_Boy
I share Nakatani's skepticism of the US WW2 nuclear weapons program, but I don't know what to make of post-WW2 nuclear weapons testing. I agree with him that "fusion" or "hydrogen" bombs require a fission (Uranium or Plutonium) reaction to start. Thus if fission bombs are fake, fusion bombs must also be fake. Conversely, if fusion bombs are real, (some) fission bombs must also be real.
Possibly U-235 bombs are fake, but Pu-239 bombs are real. Nuclear weapons require a supercritical reaction (ie a nuclear chain reaction which is increasing in rate of reaction) powered by "fast" neutrons. Plutonium is about twice as reactive to "fast" neutrons as Uranium, according to Wiki. https://en.wikipedia.org/wiki/Neutron_cross-section
Plutonium also emits more neutrons when it fissions.
However, casting some doubt on Plutonium supercritical explosions is the history of "supercritical" accidents which produced no nuclear explosion. Chernobyl's reactor went supercritical but produced enough heat to cause a chemical explosion (by splitting water and producing a cloud of hydrogen) rather than a nuclear one. Similar was Fukushima, where again the reactor produced hydrogen leading to a small chemical explosion. Nakatani highlights the "demon core" incidents, in which a mass of Plutonium was accidentally joined that was large enough to sustain a chain reaction and bathed researchers in radiation. No dramatic release of heat is reported. In the Cecil Kelley accident, Plutonium in a chemical mixer reached critical mass, releasing a burst of radiation as well as light. https://en.wikipedia.org/wiki/Cecil_Kelley_criticality_accident However, there is no mention of excessive heat being released, and certainly nothing that resembles a nuclear explosion.
One final thing I've uncovered in my (admittedly cursory) research into the topic is the issue of critical mass. How much nuclear material must be assembled in order to cause a nuclear chain reaction? According to Wiki, "fast" reactors (which use the same sort of neutron reaction as bombs) require a "much higher" amount of material than "thermal" reactors (because the neutrons emitted directly from fission are moving too fast to be captured by the fuel). https://en.wikipedia.org/wiki/Fast_reactor And I can't find it now but I've seen estimates that the critical mass for a thermal-neutron nuclear reactor is on the order of tons. Here for example it's claimed that a typical fuel load is 100 tons https://www.nuclear-power.com/nuclear-power-plant/nuclear-fuel/fuel-consumption-of-conventional-reactor/ but this doesn't mean that this mass is barely critical.
The CP-1 "reactor" for example was just an enormous pile of Uranium, over 45 tons of the stuff. https://en.wikipedia.org/wiki/Chicago_Pile-1 Given that Pu239 is about 6-7 times as (fast neutron) reactive as U239 this indicates a diameter 1/7th as large and thus a mass around 1 ton to achieve a Plutonium supercritical state. In comparison Fat Man officially held 6 kilograms of fissile material. https://en.wikipedia.org/wiki/Fat_man