Errors on backend since updating

I now see many errors on the backend of my site after updating my theme. I have pasted them below. Any idea what's causing this? If I disable all plugins and use a default theme, the errors go away. (The first two errors in the list are regarding Go Daddy Managed Wordpress plugins - I am not super concerned with those.)

Deprecated: Constant FILTER_SANITIZE_STRING is deprecated in /var/www/wp-content/mu-plugins/gd-system-plugin/includes/class-debug-mode.php on line 113

Deprecated: Constant FILTER_SANITIZE_STRING is deprecated in /var/www/wp-content/mu-plugins/gd-system-plugin/includes/class-debug-mode.php on line 114

Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated in /var/www/wp-includes/functions.php on line 7035

Deprecated: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in /var/www/wp-includes/functions.php on line 2164

Deprecated: Return type of Requests_Cookie_Jar::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Cookie/Jar.php on line 63

Deprecated: Return type of Requests_Cookie_Jar::offsetGet($key) should either be compatible with ArrayAccess::offsetGet(mixed $offset): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Cookie/Jar.php on line 73

Deprecated: Return type of Requests_Cookie_Jar::offsetSet($key, $value) should either be compatible with ArrayAccess::offsetSet(mixed $offset, mixed $value): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Cookie/Jar.php on line 89

Deprecated: Return type of Requests_Cookie_Jar::offsetUnset($key) should either be compatible with ArrayAccess::offsetUnset(mixed $offset): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Cookie/Jar.php on line 102

Deprecated: Return type of Requests_Cookie_Jar::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Cookie/Jar.php on line 111

Deprecated: Return type of Requests_Utility_CaseInsensitiveDictionary::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Utility/CaseInsensitiveDictionary.php on line 40

Deprecated: Return type of Requests_Utility_CaseInsensitiveDictionary::offsetGet($key) should either be compatible with ArrayAccess::offsetGet(mixed $offset): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Utility/CaseInsensitiveDictionary.php on line 51

Deprecated: Return type of Requests_Utility_CaseInsensitiveDictionary::offsetSet($key, $value) should either be compatible with ArrayAccess::offsetSet(mixed $offset, mixed $value): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Utility/CaseInsensitiveDictionary.php on line 68

Deprecated: Return type of Requests_Utility_CaseInsensitiveDictionary::offsetUnset($key) should either be compatible with ArrayAccess::offsetUnset(mixed $offset): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Utility/CaseInsensitiveDictionary.php on line 82

Deprecated: Return type of Requests_Utility_CaseInsensitiveDictionary::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/wp-includes/Requests/Utility/CaseInsensitiveDictionary.php on line 91

Deprecated: http_build_query(): Passing null to parameter #2 ($numeric_prefix) of type string is deprecated in /var/www/wp-includes/Requests/Transport/cURL.php on line 345

Warning: Cannot modify header information - headers already sent by (output started at /var/www/wp-includes/Requests/Utility/CaseInsensitiveDictionary.php:15) in /var/www/wp-admin/admin-header.php on line 9