<?php
$tag = "MU";
$string = 'D109 MU, worked from home today
Walked the dog, later took the kids to swimming. D110 MU. Went to the gym in the evening for the 9th time this month.';
var_export(preg_match_all("~D\K\d+(?= $tag)~", $string, $out) ? $out[0] : 'fail');
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
array (
0 => '109',
1 => '110',
)