@Fuseteam thanks for the suggestion. Let me look into it.

@Vlad-Nirky I don't know which kernel version I was running back then. But I know that both sim cards were being detected and noble was still in beta at the time.
When noble was announced I decided to give UT touch another go and here we are.

@Vlad-Nirky I don't think it's a regression. I'm not sure how the UT images are baked or how the install process is done by the installer. But it's obvious that I have a Redmi Note 9 kernel instead of a Redmi 9 one.
Maybe there was a mixup and somehow the install script is being instructed to flash a wrong kernel image.
In android lingo, flashing the correct boot.img in fastboot would have fixed the issue.
I guess it's upon the device maintainer to answer these maybes.

Below are two screenshots taken months apart. One while using UT on focal and one that I took yesterday. Look at the network indicators. One shows two while the other one shows one.

@Vlad-Nirky If I remember correctly, UT supported two sim cards on lancelot, just that you couldn't use the second sim card for mobile data like it says on the devices page. But you could make and receive calls using both sim cards.
Also, merlin is not lancelot.

Hi guys.. New here. I flashed Ubports on my lancelot (24.04-1.0 Stable) a few hours ago and I noticed that sim 2 wasn't being detected. Last time I flashed ubports (focal) a few months ago both sims were being detected.
So I went digging around and saw that the running kernel is 4.14.355-openela-merlin, which I don't think is the correct one- I correctly selected lancelot while installing. I used the ubports installer in windows 10.
Under imei only one imei is listed, the other one just has 'none'