D7.100 and php8.2 with mimemail failing to display html

Almost certainly this is due to bad message headers. Please attach a text file with your unformatted raw message headers.

#3261886: html tags not interpreted →
🐛 PhpMail : broken mail headers in PHP 8.0+ because of LF characters Fixed

In short though, Drupal core changes line terminators in the headers to try to fix and avoid long-standing problems with PHP using the wrong line terminators, but in PHP 8.2 this got changed. I know we fixed this in Drupal core 9+ a long time ago but I don't know about D7...

Thanks for a reply @TR! Revealed code from the first part of the email attached (I assume this is what you're after?).

Yes, that's what I was looking for. This is the problem I thought.

I did a search and found it was never fixed in core Drupal 7. See 🐛 [D7] PhpMail : broken mail headers in PHP 8.0+ because of LF characters Needs work . There's a patch in that issue which should fix the problem for you

Many thanks @TR. I applied the patch to fix the issue, but it turns out it was caused by a faulty mimemail template in the theme folder. Long story short, I am switching back to php 7.4 as there seems to be fewer issues with the several custom modules I inherited.
I appreciate the suggested fix though - thank you.
Martin