I was just coming over to ask the same question - but I sadly think it is. It is a great tiny "engine" to work with and I played around with it a lot - but it doesn't seem to be updated anymore. The creator, cstoquer, hasn't posted in ages on Twitter/X or commited anything on github on at all for quite some time now...
Viewing post in Is Pixelbox dead?
I'd say when you're already familiar with Pico-8 and if you like JS (or even TypeScript) you should check out Tic80. The free version is already quite feature rich but the pro version ($10) also allows external Code-Editor like VSCode which enables you to use the Tic80 TypeScript template and exporting to a standalone game.
Its still limited like Pico-8 but way less than that. With its "Fantasy-Console" nature you obviously have all tools in one environment.