In addition to Vue's GitHub releases page indicated in the other answer, there are other options to determine the available versions of Vue.
Option 1: NPM version page
Use Vue's NPM version page. The version numbers listed in the "Version" column can be copied exactly into the URL for unpkg.com, as they use the same versioning from NPM (e.g., https://unpkg.com/vue@3.2.26). The same is true for the tags, such as latest, next, and beta (e.g., https://unpkg.com/vue@beta resolves to https://unpkg.com/vue@3.2.0-beta.8 as of this writing).
Option 2: Unpkg's browse-package page
Use the version dropdown on unpkg.com's browse-package page at https://unpkg.com/vue/ (note the trailing slash) or https://unpkg.com/browse/vue/:
Option 3: Command line with npm info
Use npm info vue versions to quickly list all available Vue versions on the command line:
$ npm info vue versions
[
'0.0.0', '0.6.0', '0.7.0',
'0.7.1', '0.7.3', '0.7.4',
'0.7.5', '0.7.6', '0.8.0',
'0.8.1', '0.8.2', '0.8.3',
'0.8.4', '0.8.6', '0.8.7',
'0.8.8', '0.9.0', '0.9.1',
'0.9.2', '0.9.3', '0.10.0',
'0.10.1', '0.10.2', '0.10.3',
'0.10.4', '0.10.5', '0.10.6',
'0.11.0-rc', '0.11.0-rc2', '0.11.0-rc3',
'0.11.0', '0.11.1', '0.11.2',
'0.11.3', '0.11.4', '0.11.5',
'0.11.6', '0.11.7', '0.11.8',
'0.11.9', '0.11.10', '0.12.0-beta1',
'0.12.0-beta2', '0.12.0-beta3', '0.12.0-beta4',
'0.12.0-beta5', '0.12.0-csp', '0.12.0-rc',
'0.12.0-rc2', '0.12.0', '0.12.1-csp',
'0.12.1-csp.1', '0.12.1-csp.2', '0.12.1',
'0.12.2', '0.12.3', '0.12.4',
'0.12.5-csp', '0.12.5', '0.12.6-csp',
'0.12.6', '0.12.7-csp', '0.12.7',
'0.12.8-csp', '0.12.8', '0.12.9-csp',
'0.12.9', '0.12.10-csp', '0.12.10',
'0.12.11-csp', '0.12.11', '0.12.12-csp',
'0.12.12', '0.12.13-csp', '0.12.13',
'0.12.14-csp', '0.12.14', '0.12.15-csp',
'0.12.15', '0.12.16-csp', '0.12.16',
'1.0.0-alpha.1', '1.0.0-alpha.2', '1.0.0-alpha.3',
'1.0.0-alpha.4', '1.0.0-alpha.5', '1.0.0-alpha.6',
'1.0.0-alpha.7', '1.0.0-alpha.8', '1.0.0-beta.1',
'1.0.0-beta.2', '1.0.0-beta.3', '1.0.0-beta.4',
'1.0.0-csp', '1.0.0-migration', '1.0.0-rc.1',
'1.0.0-rc.2', '1.0.0-rc.2-migration', '1.0.0',
'1.0.1', '1.0.2', '1.0.3',
'1.0.4', '1.0.5', '1.0.6',
'1.0.7', '1.0.8', '1.0.9',
'1.0.10-csp', '1.0.10', '1.0.11-csp',
'1.0.11', '1.0.12-csp', '1.0.12-csp-1',
'1.0.12', '1.0.13-csp', '1.0.13',
'1.0.14-csp', '1.0.14', '1.0.15-csp',
'1.0.15', '1.0.16-csp', '1.0.16',
'1.0.17-csp', '1.0.17', '1.0.18-csp',
'1.0.18', '1.0.19-csp', '1.0.19',
'1.0.20-csp', '1.0.20', '1.0.21-csp',
'1.0.21', '1.0.22-csp', '1.0.22',
'1.0.23-csp', '1.0.23', '1.0.24-csp',
'1.0.24', '1.0.25-csp', '1.0.25',
'1.0.26-csp', '1.0.26', '1.0.27-csp',
'1.0.27', '1.0.28-csp', '1.0.28',
'2.0.0-alpha.1', '2.0.0-alpha.2', '2.0.0-alpha.3',
'2.0.0-alpha.4', '2.0.0-alpha.5', '2.0.0-alpha.6',
'2.0.0-alpha.7', '2.0.0-alpha.8', '2.0.0-beta.1',
'2.0.0-beta.2', '2.0.0-beta.3', '2.0.0-beta.4',
'2.0.0-beta.5', '2.0.0-beta.6', '2.0.0-beta.7',
'2.0.0-beta.8', '2.0.0-rc.1', '2.0.0-rc.2',
'2.0.0-rc.3', '2.0.0-rc.4', '2.0.0-rc.5',
'2.0.0-rc.6', '2.0.0-rc.7', '2.0.0-rc.8',
'2.0.0', '2.0.1', '2.0.2',
'2.0.3', '2.0.4', '2.0.5',
'2.0.6', '2.0.7', '2.0.8',
'2.1.0', '2.1.1', '2.1.2',
'2.1.3', '2.1.4', '2.1.5',
'2.1.6', '2.1.7', '2.1.8',
'2.1.9', '2.1.10', '2.2.0-beta.1',
'2.2.0-beta.2', '2.2.0', '2.2.1',
'2.2.2', '2.2.3', '2.2.4',
'2.2.5', '2.2.6', '2.3.0-beta.1',
'2.3.0', '2.3.1', '2.3.2',
'2.3.3', '2.3.4', '2.4.0',
'2.4.1', '2.4.2', '2.4.3',
'2.4.4', '2.5.0', '2.5.1',
'2.5.2', '2.5.3', '2.5.4',
'2.5.5', '2.5.6', '2.5.7',
'2.5.8', '2.5.9', '2.5.10',
'2.5.11', '2.5.12', '2.5.13',
'2.5.14', '2.5.15', '2.5.16',
'2.5.17-beta.0', '2.5.17', '2.5.18-beta.0',
'2.5.18', '2.5.19', '2.5.20',
'2.5.21', '2.5.22', '2.6.0-beta.1',
'2.6.0-beta.2', '2.6.0-beta.3', '2.6.0',
'2.6.1', '2.6.2', '2.6.3',
'2.6.4', '2.6.5', '2.6.6',
'2.6.7', '2.6.8', '2.6.9',
'2.6.10', '2.6.11', '2.6.12',
'2.6.13', '2.6.14', '3.0.0-alpha.0',
'3.0.0-alpha.1', '3.0.0-alpha.2', '3.0.0-alpha.3',
'3.0.0-alpha.4', '3.0.0-alpha.5', '3.0.0-alpha.6',
'3.0.0-alpha.7', '3.0.0-alpha.8', '3.0.0-alpha.9',
'3.0.0-alpha.10', '3.0.0-alpha.11', '3.0.0-alpha.12',
'3.0.0-alpha.13', '3.0.0-beta.1', '3.0.0-beta.2',
'3.0.0-beta.3', '3.0.0-beta.4', '3.0.0-beta.5',
'3.0.0-beta.6', '3.0.0-beta.7', '3.0.0-beta.8',
'3.0.0-beta.9', '3.0.0-beta.10', '3.0.0-beta.11',
'3.0.0-beta.12', '3.0.0-beta.13', '3.0.0-beta.14',
'3.0.0-beta.15', '3.0.0-beta.16', '3.0.0-beta.17',
'3.0.0-beta.18', '3.0.0-beta.19', '3.0.0-beta.20',
'3.0.0-beta.21', '3.0.0-beta.22', '3.0.0-beta.23',
'3.0.0-beta.24', '3.0.0-rc.1', '3.0.0-rc.2',
'3.0.0-rc.3', '3.0.0-rc.4', '3.0.0-rc.5',
'3.0.0-rc.6', '3.0.0-rc.7', '3.0.0-rc.8',
'3.0.0-rc.9', '3.0.0-rc.10', '3.0.0-rc.11',
'3.0.0-rc.12', '3.0.0-rc.13', '3.0.0',
'3.0.1', '3.0.2', '3.0.3',
'3.0.4', '3.0.5', '3.0.6',
'3.0.7', '3.0.8', '3.0.9',
'3.0.10', '3.0.11', '3.1.0-beta.1',
'3.1.0-beta.2', '3.1.0-beta.3', '3.1.0-beta.4',
'3.1.0-beta.5', '3.1.0-beta.6', '3.1.0-beta.7',
'3.1.0', '3.1.1', '3.1.2',
'3.1.3', '3.1.4', '3.1.5',
'3.2.0-beta.1', '3.2.0-beta.2', '3.2.0-beta.3',
'3.2.0-beta.4', '3.2.0-beta.5', '3.2.0-beta.6',
'3.2.0-beta.7', '3.2.0-beta.8', '3.2.0',
'3.2.1', '3.2.2', '3.2.3',
'3.2.4', '3.2.5', '3.2.6',
'3.2.7', '3.2.8', '3.2.9',
'3.2.10', '3.2.11', '3.2.12',
'3.2.13', '3.2.14', '3.2.15',
'3.2.16', '3.2.17', '3.2.18',
'3.2.19', '3.2.20', '3.2.21',
'3.2.22', '3.2.23', '3.2.24',
'3.2.25', '3.2.26'
]