I know you have a tough job here, but upgrading in place is like playing Russian Roulette. Eventually you will try an upgrade that corrupts your instance so it won't start and you cannot roll back. Been there done that.
If you work in the EU then keeping old versions of SQL running can be considered as a GDPR violation. For GDPR compliance you need to be on the latest version and latest fixes of all software.
Where I work our HR vendor was moaning about not wanting to do SQL2017 support. Our IT Head told them we needed SQL2017 for compliance, did they still want us as a customer. The same days they confirmed they would support SQL2017 for their current software.
Original author: https://github.com/SQL-FineBuild/Common/wiki/ 1-click install and best practice configuration of SQL Server 2019, 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005.
When I give food to the poor they call me a saint. When I ask why they are poor they call me a communist - Archbishop Hélder Câmara