Example: é is "altgr+e", ç is "altgr+", while Ω is "right-ctrl, shift+w" and ⁶ is "right-ctrl,^,6" etc.
You can do it all with the compose key. But for typing in french I find altgr+e to be faster than "rightctrl,',e".
Especially when it’s not printed on your keyboard.
https://sites.psu.edu/symbolcodes/windows/codealt/
Note that you can't just do an accent and apply it to any character (like compose). You have to put in the code for the accented character.
e.g. "a acute unicode" yields https://www.compart.com/en/unicode/U+00E1
So ‘ then a would become á
Why isn't it altgr+(letter) and repeated presses like holding down the letter on an Android mobile phone touch keyboard?
If you have a 104 key (US, wide return) keyboard layout, you can try the US international layout. In that case, shift-~ will get you ` and you can use the same compose rules as above.
Works like a charm in pretty much any program and keyboard layout.
For the more common acute/grave/.. letters, I use
setxkbmap -layout latin,<local layout> -variant ,qwerty -option grp:switch,grp:alt_shift_toggle