can't open premiere - OS woes?

I am mainly editing with Resolve these days and using it for color correction . I'm getting into  working as a colorist but that means interfacing with editors who use Premiere Pro and round tripping from Premiere to Resolve and back - Common workflow) . So I had a friend give me a program in premiere to practice the round trip with so I really know what I'm doing - and bought Premiere on a monthly basis so i can learn the round trip well. I could color correct in premiere if I need to but I need to learn this process and even if I stick in premiere the following issue will come up  anyway. 

 However I can't get Premiere to open  . I get a spinning  nothing that just says "Please wait for a moment" forever. I'm guessing  its hardware

I have an old  2017 iMac (top of the line for its time) - 27" 5K Retina iMac, 4.2Ghz i7, 64G Memory, Radeon Pro 580 8GB, 1TB SSD internal . Works fine for  Resolve in 4K so I'm sure it can handle  Premiere, but I'm still running Mojave  - Mac OS 10.14.6. I'm guessing that's the problem as Adobe says minimum  requirement is OS 11.

(I  prefer to stay in OS10.14.6 because I have some old software I like.)

Questions:

1.  Can I install an older  version of Premiere that will work on OS 10.14.6 ? If so How?

2. If so, the project file my friend gave me was done on an up to date  version of Premiere. Can  it open in an older version , or can he  change it to open in an older version ?  How?

3. Assuming 1& 2 won't work -  Can I just make a bootable SSD drive with a newer OS and boot my Mac from there and now use  Premiere ?

 4- Or am I better off doing the opposite - upgrading the internal drive and making an alternate bootable with 10.14.6 on it?

 5- If I  create a new boot drive or upgrade my existing , do I need to go further than OS 11 to use the latest version of Premiere? 

Thanks Lenny