解决办法
临时解决办法（简单粗暴）
修改/ios/Podfile注释掉Flipper相关的内容。

# Enables Flipper.
#
# Note that if you have use_frameworks! enabled, Flipper will not work and
# you should disable the next line.
#use_flipper!()

#post_install do |installer|
#react_native_post_install(installer)
#end

方法二(推荐)

修改/ios/Podfile 内容如下：

详细修改操作：
注释掉下面内容：

use_flipper!()

post_install do |installer|

　　react_native_post_install(installer)

end

并把此处替换为：

#⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄修复iOS 14.5新建RN0.64无法运行⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄
def find_and_replace(dir, findstr, replacestr)
Dir[dir].each do |name|
text = File.read(name)
replace = text.gsub(findstr,replacestr)
if text != replace
puts “Fix: ” + name
File.open(name, “w”) { |file| file.puts replace }
STDOUT.flush
end
end
Dir[dir + ‘*/’].each(&method(:find_and_replace))
end

post_install do |installer|
flipper_post_install(installer)
find_and_replace(“Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h”,
“atomic_notify_one(state)”, “folly::atomic_notify_one(state)”)

find_and_replace(“Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h”,
“atomic_wait_until(&state, previous | data, deadline)”, “folly::atomic_wait_until(&state, previous | data, deadline)”)
end
#⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃修复iOS 14.5新建RN0.64无法运行⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃

最终文件如下：

require_relative ‘../node_modules/react-native/scripts/react_native_pods’
require_relative ‘../node_modules/@react-native-community/cli-platform-ios/native_modules’

platform :ios, ‘10.0’

target ‘speed2’ do
config = use_native_modules!

use_react_native!(
:path => config[:reactNativePath],
# to enable hermes on iOS, change `false` to `true` and then install pods
:hermes_enabled => false
)

target ‘speed2Tests’ do
inherit! :complete
# Pods for testing
end

# Enables Flipper.
#
# Note that if you have use_frameworks! enabled, Flipper will not work and
# you should disable the next line.
#use_flipper!()

#post_install do |installer|
# react_native_post_install(installer)
#end

#⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄修复iOS 14.5新建RN0.64无法运行⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄⌄
def find_and_replace(dir, findstr, replacestr)
Dir[dir].each do |name|
text = File.read(name)
replace = text.gsub(findstr,replacestr)
if text != replace
puts “Fix: ” + name
File.open(name, “w”) { |file| file.puts replace }
STDOUT.flush
end
end
Dir[dir + ‘*/’].each(&method(:find_and_replace))
end

post_install do |installer|
flipper_post_install(installer)
find_and_replace(“Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h”,
“atomic_notify_one(state)”, “folly::atomic_notify_one(state)”)

find_and_replace(“Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h”,
“atomic_wait_until(&state, previous | data, deadline)”, “folly::atomic_wait_until(&state, previous | data, deadline)”)
end
#⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃修复iOS 14.5新建RN0.64无法运行⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃⌃
end

总结

方法二最终实现思路就是修改这个DistributedMutex-inl.h文件达到修复无法启动的问题。

修改/ios/Podfile注释掉Flipper相关的内容。

• 修改/ios/Podfile注释掉Flipper相关的内容。
• 删除/ios/Pod目录
• 删除/ios/Podfile.lock
• 执行 pod install --verbose
• yarn ios运行项目
• 运行成功！