the updates are cumulative.
on the install-iso you can not find the patches.
which update-iso did you tried to mount ? it should be named "VMware-vCenter-Server-Appliance-126.96.36.199100-15505668-patch-FP.iso" an can be downloaded at https://my.vmware.com/group/vmware/patch#search
Open VAMI Console of vCenter - https:// vcenter fqdn or IP:5480/ >>>Mount Patch ISO which one you want to apply >> Apply patch from "Update" section in VAMI Console >> Reboot vCenter.:-
Note:- Take an snapshot on vCenter if that's an Virtual Machine as well take backup of vCenter too for safe side before going to upgrade it with patch or any version upgrade.
Version Release Date VAMI/Release Notes Client/MOB/vpxd.log vCenter Appliance 6.7 Update 3c 2020-01-30 15505668 vCenter Appliance 6.7 Update 3b (188.8.131.52000) 2019-12-05 15132721 15129973 vCenter Appliance 6.7 Update 3a (184.108.40.206000) 2019-10-24 14836122 14792544 vCenter Appliance 6.7 Update 3 (220.127.116.11000) 2019-08-20 14367737 14368073 vCenter Appliance 6.7 Update 2c (18.104.22.168000) 2019-07-16 14070457 14070654 vCenter Appliance 6.7 Update 2b (22.214.171.124100) 2019-05-30 13843380 13843469 vCenter Appliance 6.7 Update 2a (126.96.36.199000) 2019-05-14 13643870 13639324
Just read this in the patch notes
IMPORTANT: You can update the vCenter Server Appliance with Photon OS patches released within one and the same Update release. Currently, you can patch the appliance with Photon OS patches only if you have updated the vCenter Server Appliance to 6.7 Update 3.
If you try to update the vCenter Server Appliance directly from an unsupported base version of 6.7 to the current Photon OS patch version, by using the vCenter Server Appliance Management Interface, you see a message No applicable update found. This is expected. You must first update the vCenter Server Appliance to version 6.7 Update 3 and then apply the selected Photon OS patch to the appliance.
Seems i need to go to Update 3 first.