Keyboards I found as I needed, or whose uses I found as I messed around, they’re quite good in their niches and have some overlap between each other, so picking just one to recommend is though, so including them all:

• Simple Keyboard I originally started using because, well, it’s simple, plus efficient and very lightweight. But also, digging around, it has quite a good range of keyboards supported, ranging through Europeean, Southeastern Asian, Middle East, Cyrillic, and possibly others I missed, though all visual inputs, no phonetic ones:
  https://ani.social/pictrs/image/7c147c8d-526d-400f-a7ec-36255e01b69f.webp
  https://ani.social/pictrs/image/e844be4f-f6f3-4bc8-811a-3e49423e0a23.webp
  https://ani.social/pictrs/image/837797fe-81ff-4776-9074-a7980a45a03e.webp

• Mozc is mostly specific for Japanese. It is another visual keyboard, and you swipe through the hiragana keys and the keyboard suggests possible writings in kanji and katakana too:
  https://ani.social/pictrs/image/9c94d4e1-796b-4bac-8515-b3846efaca56.webp

• Heliboard I use because it was the first decent Korean keyboard I found, a visual one where you build syllables through the hangul radicals. But upon further inspection, and some tests, it has a good range of languages, like Simple Keyboard:
  https://ani.social/pictrs/image/f8256cec-c073-4d40-9335-53b3f3a93604.webp
  https://ani.social/pictrs/image/5b38c7e9-eb44-464b-a756-d70ad94e672e.webp

• Fcitx5 is the only phonetic only I found, but it can be useful specially if learning the languages supported. And though technically it isn’t necessarily a phonetic keyboard, from what I tested, that is how it is the most reliable, as the keys remain as the English default. And of the languages supported, through plugins that is, they are mainly Southeastern Asian ones, as well as having a similar suggestion feature as Mozc:
  https://ani.social/pictrs/image/237b6098-669d-45db-b27a-292e871bb03d.webp
  https://ani.social/pictrs/image/81dfe08a-db82-48d3-9bba-bb4aa66a004d.webp