You mean for text fields in the game?
• If you want to use such things regularly, it’s probably easier to enable the relevant layout.
• If not, using Compose button is slower, ḅüť 🅸🆃 ãĺļóŵṣ lots of ⓕ🄐🄽©ẙ symbols (just tested in OXCE 7.8.7 — works for me). ☺ Practically, however, it’s up to the font. Which is awesome compared to DOS, but as Unicode goes, almost modest. So the Greek letters, Roman numerals and « » † ‡ ← → ↑ ↓ © ♂ ♀ ≡ ≪ ≫ ¡ ¿ ∧ ∨ ∩ ∪ ⊂ ⊃ ∈ ∋ are supported, but × ≈ ≤ ≥ 〈 〉 ∉ ∌ ‼ ⁈ — ⌀ ⯐ ⌁ ⚡ ☢ ☣ ⚛ ⛏ ⚒ ⚓ ⚕ ☤ are replaced with question marks and characters >2 bytes (🕏 🌡 🎃 ) are ignored. For some reason, ½ ¼ are replaced with tiny dots, but ⅓ ⅕⅙ ⅐ ⅛ ⅟ with question mark.