PS /> git branch --format='{"name":"%(refname:lstrip=2)"}' --list

%(refname:lstrip=2)

{"name":"main"}
{"name":"feature-branch-a"}
{"name":"feature-branch-b"}
,...

PS /> git branch --format='{"name":"%(refname:lstrip=2)","isMainBranch":'"$(if [[ $(git symbolic-ref --short HEAD) == "main" ]]; then echo true; else echo false; fi)"' }' --list

ParserError:
Line |
   1 |  … --format='{"name":"%(refname:lstrip=2)","isMainBranch":'"$(if [[ $(gi …
     |                                                                 ~
     | Missing '(' after 'if' in if statement.

'"`$(if [[ `$

{"name":"main","isMainBranch":$(if [[ $(git symbolic-ref --short HEAD) == main ]]; then echo true; else echo false; fi) }
{"name":"feature-branch-a","isMainBranch":$(if [[ $(git symbolic-ref --short HEAD) == main ]]; then echo true; else echo false; fi) }
{"name":"feature-branch-b","isMainBranch":$(if [[ $(git symbolic-ref --short HEAD) == main ]]; then echo true; else echo false; fi) }

$branches = git branch | ForEach-Object {
    $default = $false
    $activeBranch = git symbolic-ref --short HEAD
    $currentBranch = ($_.Replace("* ", " ")).Trim()
    if ($currentBranch -eq $activeBranch) {
        $default = $true
    }
    @{
        name            = $currentBranch
        isMainBranch = $default
    } | ConvertTo-Json
} | ConvertFrom-Json