I didn't find any htaccess files in the install.
this file is actually named, ".htaccess"
This file wont be within the UBB.threads install package. Its something that may be within your directory which is reporting PHP 5.6. UBB.threads does not make or include this file.http://www.htaccess-guide.com/
Running php -v from the commandline shows I'm running 7.2.10. Php.info file says the same thing. How do I enable debugging?
phpinfo will tell you exactly the system variables which it receives. Debugging will also display the PHP version number in the footer. As an example, it will display something simular to this:
PHP: 7.3.7 Page Time: 0.164s Queries: 15 (0.010s) Memory: 2.6524 MB (Peak: 2.7701 MB) Data Comp: Off Server Time: 2019-07-14 01:04:59 UTC
Valid HTML 5 and Valid CSS
To Enable debugging:
Control Panel > Primary: Enable Debugging
It should be turned off when you're done.
If you are already on the expected version of PHP, then you're all set
If not, then you may need to contact your webhost for further support. PHP version switching is not something within the relm of UBB.threads support.