Yes I have a valid vB licence for my domain since vb2 release.
I don't want to move to vB4 or 5, and lack of php 7.2 support is starting to be problematic.
I'm not aware of encrypted php version of vb, as far as I know, all the php files I download from member area are tagged with my customer number, but unencrypted.
Finally, since I have access to my PHP files and vb templates, I'm simply looking for one guideline of modifications to be applied to make my own vb 3.8.11 compatible with php 7.2
(I decided not to download any build of vBulletin from customer area despite that I have the license, this is to make sure I am clean with my license.)
Supposing that your downloaded source code of vBulletin 3.8.11 from vBulletin official is not zend encrypted: You can find an online PHP grammar checker (e.g. https://phpcodechecker.com) and check through PHP files and fix them one by one. After that, check both the language xml and the template xml: find all condition expressions and make sure that all constants used in these expressions are not like [constant] but like ['constant']. If not, gzip-compressed pages of vBulletin may return to either a blank page or crashed webpage to your web browser. If these are enough, then I guess you can use it with MariaDB (at least 10.4.x).
(Please stay away from MySQL 8 due to its SQL syntax changes, unless you update vBulletin source code to use new syntax and the new stronger password encryption system.)