I haven’t cross-checked this with Forge CLI 5.0.0 yet, just quickly as additional input for those investigating - the various errors discussed here sound remarkably similar to what has been discussed for the Forge CLI 1.6.0 update in April 2021, here’s our summary:
The TL;DR is that we had to deviate from the instructions and use install @forge/cli@2.0.1 --omit optional to avoid the errors stemming from the back then optional keytar dependency, though IIRC that problem had been partially mitigated by the Forge team in a later CLI version.
Of course, the scope of the major release at hand seems to be to now require a local keychain, which means the never fully addressed problem around that dependency could now be a significant hurdle or even blocker depending on the target environment.