ED: The limit of XP in the unmodded game series is:
Baldur's Gate with TOSC 161,000 (Roughly level 8-10, the classes in 2e have different XP requirements to level up, even more, the multiclass have half of it )
Baldur's Gate: Siege of Dragonspear 500,000 (level 10-12 in pure classes, half in multiclass)
Baldur's Gate II: Shadows of Amn 2,950,000 (level 17-19, but you start with a level 7-12 character)
Baldur's Gate II: Throne of Bhaal 8,000,000 (The top is level 40 for single-class rogues, monks, clerics, and fighters. It is impossible for other slow-leveling classes or multiclass/dual class.
Even more, you do not reach that level in the OC without using some insane grinding and/or mods)https://baldursgate.fandom.com/wiki/Experience_Tables
In nwn2 OC the maximum level is 20, and if you reach it is because the final battles give a lot of XP. You level up two-four times in the last chapter.
In ToEE the level cap is 10, but I think it is too restrictive, and ToEE is a very short game anyway. Knighs of the Chalice and Pool of radiance takes you from level 1 to 19-20 tops. IWD series has no limits but also no epic skills in IWD2 and you can reach it only in HOF, NG+
In P:K you have a limit of LVL 20 too, but in that game, it is a really steep curve from level 12 and beyond. I usually beat the game with a party of level 16-17 tops. You do not reach level 20 without the DLC and usually only solo chars in the final chapter.
I do not think you will reach epic levels until an expansion or the next game in the series, they usually do that.