Can't display the simplest UIToolbar

I thought I could easily display a toolbar in UIKit, but I was wrong, or at least I can't do so without getting "Unable to simultaneously satisfy constraints." console messages.

Here is my code:

import UIKit

class ViewController: UIViewController {
    let toolbar = UIToolbar()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .systemBackground
        
        toolbar.items = [
            UIBarButtonItem(title: "Title", style: .plain, target: nil, action: nil),
            UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
        ]
        view.addSubview(toolbar)
        toolbar.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            toolbar.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
            toolbar.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            toolbar.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
            toolbar.heightAnchor.constraint(equalToConstant: 44)
        ])
    }
}

And here is the console log:

Unable to simultaneously satisfy constraints.
	Probably at least one of the constraints in the following list is one you don't want. 
	Try this: 
		(1) look at each constraint and try to figure out which you don't expect; 
		(2) find the code that added the unwanted constraint or constraints and fix it. 
	(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x600002107b10 h=--& v=--& _UIToolbarContentView:0x104008e40.height == 0   (active)>",
    "<NSLayoutConstraint:0x600002122e90 V:|-(0)-[_UIButtonBarStackView:0x10250d8b0]   (active, names: '|':_UIToolbarContentView:0x104008e40 )>",
    "<NSLayoutConstraint:0x600002121ef0 _UIButtonBarStackView:0x10250d8b0.bottom == _UIToolbarContentView:0x104008e40.bottom   (active)>",
    "<NSLayoutConstraint:0x600002107a70 UIButtonLabel:0x10250f280.centerY == _UIModernBarButton:0x1027059c0'Title'.centerY + 1.5   (active)>",
    "<NSLayoutConstraint:0x60000210ea30 'TB_Baseline_Baseline' _UIModernBarButton:0x1027059c0'Title'.lastBaseline == UILayoutGuide:0x600003b0ca80'UIViewLayoutMarginsGuide'.bottom   (active)>",
    "<NSLayoutConstraint:0x60000210ea80 'TB_Top_Top' V:|-(>=0)-[_UIModernBarButton:0x1027059c0'Title']   (active, names: '|':_UIButtonBarButton:0x102607120 )>",
    "<NSLayoutConstraint:0x60000210e8f0 'UIButtonBar.maximumAlignmentSize' _UIButtonBarButton:0x102607120.height == UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide'.height   (active)>",
    "<NSLayoutConstraint:0x60000212c960 'UIView-bottomMargin-guide-constraint' V:[UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide']-(0)-|   (active, names: '|':_UIButtonBarStackView:0x10250d8b0 )>",
    "<NSLayoutConstraint:0x60000210ec60 'UIView-bottomMargin-guide-constraint' V:[UILayoutGuide:0x600003b0ca80'UIViewLayoutMarginsGuide']-(11)-|   (active, names: '|':_UIButtonBarButton:0x102607120 )>",
    "<NSLayoutConstraint:0x60000212d6d0 'UIView-topMargin-guide-constraint' V:|-(0)-[UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide']   (active, names: '|':_UIButtonBarStackView:0x10250d8b0 )>"
)
Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600002107a70 UIButtonLabel:0x10250f280.centerY == _UIModernBarButton:0x1027059c0'Title'.centerY + 1.5   (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.
Unable to simultaneously satisfy constraints.
	Probably at least one of the constraints in the following list is one you don't want. 
	Try this: 
		(1) look at each constraint and try to figure out which you don't expect; 
		(2) find the code that added the unwanted constraint or constraints and fix it. 
	(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x600002106710 h=--& v=--& _UIToolbarContentView:0x104008e40.width == 0   (active)>",
    "<NSLayoutConstraint:0x600002120b40 H:|-(0)-[_UIButtonBarStackView:0x10250d8b0]   (active, names: '|':_UIToolbarContentView:0x104008e40 )>",
    "<NSLayoutConstraint:0x600002122e40 H:[_UIButtonBarStackView:0x10250d8b0]-(0)-|   (active, names: '|':_UIToolbarContentView:0x104008e40 )>",
    "<NSLayoutConstraint:0x60000210eda0 'TB_Leading_Leading' H:|-(16)-[_UIModernBarButton:0x1027059c0'Title']   (active, names: '|':_UIButtonBarButton:0x102607120 )>",
    "<NSLayoutConstraint:0x60000210eb70 'TB_Trailing_Trailing' H:[_UIModernBarButton:0x1027059c0'Title']-(16)-|   (active, names: '|':_UIButtonBarButton:0x102607120 )>",
    "<NSLayoutConstraint:0x60000210e580 'UISV-canvas-connection' UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide'.leading == _UIButtonBarButton:0x102607120.leading   (active)>",
    "<NSLayoutConstraint:0x60000210e5d0 'UISV-canvas-connection' UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide'.trailing == UIView:0x10400e480.trailing   (active)>",
    "<NSLayoutConstraint:0x60000210e9e0 'UISV-spacing' H:[_UIButtonBarButton:0x102607120]-(0)-[UIView:0x10400e480]   (active)>",
    "<NSLayoutConstraint:0x60000212c820 'UIView-leftMargin-guide-constraint' H:|-(0)-[UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide'](LTR)   (active, names: '|':_UIButtonBarStackView:0x10250d8b0 )>",
    "<NSLayoutConstraint:0x60000212ca00 'UIView-rightMargin-guide-constraint' H:[UILayoutGuide:0x600003b00380'UIViewLayoutMarginsGuide']-(0)-|(LTR)   (active, names: '|':_UIButtonBarStackView:0x10250d8b0 )>"
)
Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x60000210eb70 'TB_Trailing_Trailing' H:[_UIModernBarButton:0x1027059c0'Title']-(16)-|   (active, names: '|':_UIButtonBarButton:0x102607120 )>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

I tried giving the toolbar a frame rather than constraints, and also to not give it an explicit height.

The only thing that works is to comment out UIBarButtonItem(title: "Title", style: .plain, target: nil, action: nil), which isn't really a solution.

What am I doing wrong?