Android Keyboard (AOSP) Spell Checker does only work with one language. If multiple (system) languages are selected and spell checker is set to use system languages, it will only use the first language. Word suggestions will change, when changing the keyboard language, but spell checker will not. Therefore everything written in the second language will be underlined in red and tapping them gives you suggestions in the first language.
I am facing the same issue on a POCO X3 NFC, strangely only for one of the two used SIMs.
The dev only really uses xda to post new releases, chances are this will never be read. He operates mostly on telegram, you need to find out which telegram group he communicates on. I don't use telegram so I don't know which group it is.
Oh ok, i dont use Telegramm, maybe some who read this and is in the channel can ask him for a build to get the security updates.
/* * I'm not responsible for bricked devices, dead SD cards, thermonuclear war, or you getting fired because the alarm app failed (like it did for me...). * Please do some research if you have any concerns about features included in the products you find here before flashing it! * YOU are choosing to make these modifications, and if you point the finger at me for messing up your device, I will laugh at you. * Your warranty will be void if you tamper with any part of your device / software. * Same statement for XDA. */