I can't install adobe cc and camtasia on OS X EI Capitan version 10.11.6

El Capitan is too old to run the current Adobe CC.

Older versions will run on it.

I'm not familiar with Camtasia, but any software for the Mac has spec requirements directly on the developer's website,

and many are also listed on

https://roaringapps.com/apps

If your Mac is one of the following or newer, you can upgrade via the App Store.

• MacBook (Late 2009 or newer) 6,1
• MacBook Pro (Mid 2010 or newer) 6,1
• MacBook Air (Late 2010 or newer) 3,1
• Mac mini (Mid 2010 or newer) 4,1
• iMac (Late 2009 or newer) 10,1
• Mac Pro (Mid 2010 or newer) 5,1

Where the x,y is the Machine ID as listed in your System Report or Profile in Apple menu -> About This Mac.

https://discussions.apple.com/docs/DOC-10693

explains how to get Sierra and has links also for newer operating systems.

Exactly. And as a result you can't run the current Adobe CC applications like Adobe Photoshop 2020. You'll need an older version of these programs that support High Sierra, once you upgrade to High Sierra.

https://discussions.apple.com/docs/DOC-12081

No. You can only upgrade as far as High Sierra (10.13.6) with your Late-2011 MacBook Pro.

Well, late 2011 still can't run Catalina. So you'll need to run an older version of Adobe than 2020.