Call Stack and Error Messages -- Unable to Change PHP Version

I’m new to Local, but have searched these forums for my answer to no avail. I found that upon loading my site, I got lots of ugly chart warnings / call stack info. The answer I found here is that I need to downgrade to an older PHP version so it doesn’t do this. There’s nowhere in the software (preferences, site setup, etc.) that allows for this. I read on, and saw you must create a “custom” environment, so I did this as a test.

With prefs set to default to a custom environment, I created a new test site – no options anywhere I could find to change PHP version – whether right click or elsewhere.

Everything else works great, but this is really frustrating and confusing. Here are a couple other screenshots I took:
https://flywheel-contact-uploads.s3.amazonaws.com/uploads/1574270728963-4xv5luu0f0l-e417e672170b836a2264dd09cec31862/Screen%20Shot%202019-11-20%20at%2011.23.51%20AM.png?AWSAccessKeyId=AKIAIILIZQFMMOH7EMLA&Expires=1576949158&Signature=VOeHSjFaTOFFWDRXInQ5ToaAXF0%3D
https://flywheel-contact-uploads.s3.amazonaws.com/uploads/1574270734604-wwjlwqcgq8h-e417e672170b836a2264dd09cec31862/Screen%20Shot%202019-11-20%20at%2011.25.07%20AM.png?AWSAccessKeyId=AKIAIILIZQFMMOH7EMLA&Expires=1576949158&Signature=N1zbMGu6EfhCihfrLWzBAkchqSs%3D