There's lots of untruths attributed to Ibn Taymiyyah (rh). We can see from some of his writings that he did acknowledge that Hell is eternal. One such source is the following:
"The Salaf of the Ummah and its leading scholars, and all of Ahl al-Sunnah wal-Jamaa'ah are agreed that there are from the created things those which will not cease to exist, and will never entirely perish, such as Paradise and Hellfire, the Throne and other than that. And none spoke of the expiration of all of the created things except a faction from the innovating Ahl al-Kalaam, such as al-Jahm bin Safwan and whoever agreed with him from the Mu'tazilah and their likes. (Majmu' al-Fatawa 18/307).
Islamweb explains a little on this confusion:
"..it is not true that Shaykh Al-Islam Ibn Taymiyyah may Allaah have mercy upon him said that Hell is not imperishable and nothing of this has been found in any of his printed and commonly-used books. What actually happened is that his student, Ibn Al-Qayyim may Allaah have mercy upon him reported on his authority that the righteous predecessors had two opinions concerning this issue and he mentioned some relevant citations reported on the authority of the Companions may Allaah have mercy upon them. However, in his own books, Ibn Taymiyyah may Allaah have mercy upon him confirmed the eternal nature of Paradise and Hell. He also reported the scholars’ and Imaams’ consensus on this issue.
As for those who had the opinion that Hell may eventually be empty ('empty' doesn't necessarily mean 'non-eternal') formed their view based on verses such as Hud 107 and Al An'am 128 in which Allah (ﷻ) says that people will abide there eternally "EXCEPT for what Allah wills". -- Is this opinion wrong? Yes. Would that make any scholar with this view an innovator? No, because they are drawing this Ijtihad (independent reasoning) from the texts [Qur'an]. Scholars can be wrong in their Ijtihad from time to time, because they too are only human and can err. Doesn't make them an 'innovator'. (Innovators are generally not concerned with deriving their views from the texts).