I've been using Insomnia whenever I can since before Covid. Its been nice, but ever since they started pushing accounts so aggressively, I've switched to Yaak to get back to that feel of a simple API client that prompted me to switch to Insomia in the first place. 100% recommend. https://yaak.app/
That looks appealing but the existence of a Pricing page tells me it's just a matter of time.
I have a sense that a dumb Web API testing UI application is really not that hard to get AI to implement. These apps all look about the same for a reason. So maybe there will be a prevailing FOSS option that isn't trying to monetize.