Error After Updating - Warning: Session_Name(): Cannot Change Session Name When Headers Already Sent In

Hello

Recently been updating one of the websites (not sure to what version exactly) and now getting the errors below. I can't login to the back end either, just reloads the page. I've tried the usual stuff, cleared the var/cache. Does anyone have any ideas please?

Using PHP Ver 7.4

Warning: session_name(): Cannot change session name when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 246

Warning: session_id(): Cannot change session id when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 258

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 400

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 401

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 402

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 403

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 404

Warning: session_cache_limiter(): Cannot change cache limiter when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 406

Warning: session_cache_expire(): Cannot change cache expire when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 407

Warning: session_set_cookie_params(): Cannot change session cookie parameters when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 425

Warning: session_set_save_handler(): Cannot change save handler when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 443

Warning: session_start(): Cannot start session when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 340

have same issue after restoring my old backup from 4.11.3 to 4.17.2 fresh installation.
cant enter admin panel
php 8.1

PHP Warning

Message

session_name(): Cannot change session name when headers already sent

Error at

app/Tygh/Web/Session.php, line: 239

Backtrace

File: app/Tygh/Web/Session.php
Line: 239
Function: {closure}
File: app/Tygh/Providers/SessionProvider.php
Line: 49
Function: setName
File: app/lib/vendor/pimple/pimple/src/Pimple/Container.php
Line: 118
Function: Tygh\Providers{closure}
File: init.php
Line: 143
Function: offsetGet
File: app/functions/fn.init.php
Line: 1096
Function: {closure}
File: init.php
Line: 169
Function: fn_init

You can’t use PHP 8.1 with CS-Cart 4.11.5 as support for PHP 8.1 was only added in 4.17.1… Please downgrade used PHP version to 7.3.