Zend certified PHP/Magento developer

Deprecated Functionality: when running compile

I have two Magento sites both v2.3.3
I have noticed today that I cannot run the compile function:
php -dmemory_limit=4G bin/magento setup:di:compile
I’m getting the following error:

Application code generator... 3/7 [=====>-------]  42% 18 secs 254.0 MiB
In ErrorHandler.php line 61:Deprecated Functionality: Array and string offset access syntax with curlybraces is deprecated in /home/customer/www/mystagingsite.com/public_html/vendor/magento/framework/GraphQl/Config/Element/FieldFactory.php on line 49

I have no idea why or what has caused this.
Has anyone else experienced the same and what is the issue/solution please?
PS. I changed the curly brackets in the file from { } to [ ] on line 49 of the mentioned file but then got the following error:

Application code generator... 3/7 [=====>-------]  42% 20 secs 272.0 MiB
In ErrorHandler.php line 61:
Deprecated Functionality: Unparenthesized `a ? b : c ?: d` is deprecated. 
Use either `(a ? b : c) ?: d` or `a ? b : (c ?: d)` in /home/customer/www/mystagingsite.com/public_html/vendor/magento/framework-message-queue/BatchConsumer.php on line 154

This is so odd.
Please help if you can
Andy