Scroll view constraints - programmaticaly + storyboard hack

ScrollView.m

// SnapKit(Masonry) 1
// https://github.com/SnapKit/Masonry

[self. addSubview: scrollView];
[scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
    make.edges.equalTo(safeAreaLayoutGuide);
}];

[scrollView addSubview: contentView];
[contentView mas_makeConstraints:^(MASConstraintMaker *make) {
    make.edges.equalTo(scrollView);
    make.width.equalTo(scrollView);
    make.height.equalTo(scrollView).priorityLow();
}];

// Pure autolayout

// https://monkey.work/blog/2020-11-08-uiscrollview/
// https://github.com/seifeet/SwiftFormScrolling
// https://useyourloaf.com/blog/easier-scrolling-with-layout-guides/

// VC Content view:

[self addSubview:scrollView];
scrollView.backgroundColor = UIColor.whiteColor;
scrollView.showsHorizontalScrollIndicator = YES;
scrollView.showsVerticalScrollIndicator = YES;
scrollView.isScrollEnabled = YES;

scrollView.translatesAutoresizingMaskIntoConstraints = NO;
[NSLayoutConstraint activateConstraints:@[
    [scrollView.topAnchor constraintEqualToAnchor: self.safeAreaLayoutGuide.topAnchor],
    [scrollView.bottomAnchor constraintEqualToAnchor: self.safeAreaLayoutGuide.topAnchor],
    [scrollView.leadingAnchor constraintEqualToAnchor: self.safeAreaLayoutGuide.leadingAnchor],
    [scrollView.trailingAnchor constraintEqualToAnchor: self.safeAreaLayoutGuide.trailingAnchor]
]];

[scrollView addSubview:contentView];
contentView.backgroundColor = UIColor.whiteColor;
contentView.isUserInteractionEnabled = YES;

contentView.translatesAutoresizingMaskIntoConstraints = NO;
[NSLayoutConstraint activateConstraints:@[
    [contentView.topAnchor constraintEqualToAnchor: scrollView.contentLayoutGuide.topAnchor],
    [contentView.bottomAnchor constraintEqualToAnchor: scrollView.contentLayoutGuide.bottomAnchor],
    [contentView.leadingAnchor constraintEqualToAnchor: scrollView.contentLayoutGuide.leadingAnchor],
    [contentView.trailingAnchor constraintEqualToAnchor: scrollView.contentLayoutGuide.trailingAnchor]
]];
    
NSLayoutConstraint* contentViewCenterY = [contentView.centerYAnchor constraintEqualToAnchor: scrollView.centerYAnchor];
contentViewCenterY.priority = UILayoutPriorityDefaultLow;

NSLayoutConstraint* contentViewHeight = [contentView.heightAnchor constraintGreaterThanOrEqualToAnchor: self.heightAnchor];
contentViewHeight.priority = UILayoutPriorityDefaultLow;

[NSLayoutConstraint activateConstraints:@[
    [contentView.centerXAnchor constraintEqualToAnchor: scrollView.centerXAnchor],
    contentViewCenterY,
    contentViewHeight
]];

// Storyboard:
// Height - greater that or equal to 200
// Width - equat to safearea
// + MOST IMPORTANT: update content size at viewDidAppear (or any other method where all UI is ready)
CGSize scrollContentSize = CGSizeZero;
[UIView *] subviews = self.scrollView.subviews;
// scrollView?.contentSize = self.scrollView?.subviews.reduce(CGRect.zero) { $0.union($1.frame) }.size ?? .zero
scrollview.contentSize = scrollContentSize;
scrollView.contentInset = UIEdgeInsetsMake(0.0f, 0.0f, 20.0f, 0.0f);
[scrollView layoutSubviews];

-(void) viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    scrollView.contentSize = CGSizeMake(stackView.frame.width, stackView.frame.height);    
}

ScrollView.swift

// SnapKit:
// https://github.com/SnapKit/SnapKit

addSubview(scrollView)
scrollView.snp.makeConstraints { make in
   make.edges.equalTo(safeAreaLayoutGuide.snp.edges)
}
scrollView.addSubview(contentView)
contentView.snp.makeConstraints { make in
   make.edges.equalToSuperview()
   make.width.equalToSuperview()
   make.height.equalToSuperview().priority(.low)
}

// Pure autolayout

// https://monkey.work/blog/2020-11-08-uiscrollview/
// https://github.com/seifeet/SwiftFormScrolling

// VC Content view:

addSubview(scrollView)
scrollView.backgroundColor = UIColor.white
scrollView.showsHorizontalScrollIndicator = false
scrollView.showsVerticalScrollIndicator = true
scrollView.isScrollEnabled = true

scrollView.translatesAutoresizingMaskIntoConstraints = false
let scrollViewConstraints: [NSLayoutConstraint] = [
    scrollView.topAnchor.constraint(equalTo: self.safeAreaLayoutGuide.topAnchor),
    scrollView.bottomAnchor.constraint(equalTo: self.safeAreaLayoutGuide.topAnchor),
    scrollView.leadingAnchor.constraint(equalTo: self.safeAreaLayoutGuide.leadingAnchor),
    scrollView.trailingAnchor.constraint(equalTo: self.safeAreaLayoutGuide.trailingAnchor)
]
NSLayoutConstraint.activate(scrollViewConstraints)

scrollView.addSubview(contentView)
contentView.backgroundColor = UIColor.white
contentView.isUserInteractionEnabled = true
contentView.translatesAutoresizingMaskIntoConstraints = false
let contentViewConstraints: [NSLayoutConstraint] = [
   contentView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor),
   contentView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor),
   contentView.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor),
   contentView.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.trailingAnchor)
]
NSLayoutConstraint.activate(contentViewConstraints)
        
let contentViewCenterY = contentView.centerYAnchor.constraint(equalTo: scrollView.centerYAnchor)
contentViewCenterY.priority = .defaultLow

let contentViewHeight = contentView.heightAnchor.constraint(greaterThanOrEqualTo: self.heightAnchor)
contentViewHeight.priority = .defaultLow

NSLayoutConstraint.activate([
   contentView.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor),
   contentViewCenterY,
   contentViewHeight
])

// Storyboard:
// Height - greater that or equal to 200
// Width - equat to safearea
// + MOST IMPORTANT: update content size at viewDidAppear (or any other method where all UI is ready)
scrollView?.contentSize = self.scrollView?.subviews.reduce(CGRect.zero) { $0.union($1.frame) }.size ?? .zero
scrollView?.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 20, right: 0)
scrollView?.layoutSubviews()

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    scrollView.contentSize = CGSize(width: stackView.frame.width, height: stackView.frame.height)       
}