vcenter 6.5 is quite old and general support will end this year on October 15th 2022.
Is this on purpose due to hardware restrictions or a restricted enterprise environment?
Which guest OS is affected? Windows or Linux only.
Take look here for Ubuntu.
https://linuxconfig.org/install-vmware-tools-on-ubuntu-20-04-focal-fossa-linux
or here:
https://communities.vmware.com/t5/VMware-Fusion-Discussions/VMware-tools-on-Ubuntu-64-bit-Server-20-04/td-p/2317996
Most systems detect if they are running within a VM and install openvm-tools which is more or less the open source standard today. As far as I know. Vmware tools aren't in development any more for linux because of openvm-tools they come shipped with the distro.
Is it only the window or is the resolution itself not changing. Keep in mind you have to increase vram for VM in case you need higher resolution then 1920x1080.