Hi!
My friend is looking for an Android tablet that has an unlockable bootloader and also has a custom ROM. I’ve checked a lot and every one of them is problematic. Usual brands here are Samsung, Lenovo, Huawei, Honor, TCL, Xiaomi. Apparently Huawei and Honor is out of question since they don’t allow unlocking bootloader. TCL is new so no ROMs. Xiaomi seems possible but unlocking a Xiaomi device recently became even more pain.
Do you know a decent model from these brands? Preferably 10-12 inch screen.
Try Pixel Tablet based on Pixel 7 chipset. All pixel device have easily unlockable bootloader with ability to use AVB on custom ROMs and 7 years of support. You can install GrapheneOS on it which is the best ROM in terms of security & privacy and have all features that LineageOS has (+ sandboxed Google Play). It also support USI 2.0 styluses.
Well, that would be my first recommendation if they sold them here.