I deleted the Normal.dot template and word recreated it from scratch, and I was after a while able to add the word spell checker to my 2022 Studio, but not the 2022 Beta, which is really very very strange! One thing you can also try is to open any document, go to options, proofreading, then choose to Recheck Spelling in that document, and somehow it does something to the spell checker that would allow it to work. I will just have to restart my PC now to verify if this is resolved for good or not. 

Is there a plan to fix this issue in Studio? The pain has lasted way too long...

Indeed Jussi as Hunspell fails so many languages like yours and mine (Arabic)! I hope a solution comes fast enough to save the day for us. 

Hunspell is terrible. Period. I now work without my beloved macros in order to be able to use Word spellcheck.
One reason not to use Hunspell is that customers require me to do a spellcheck before delivery, and if they afterwards find something with Word spellcheck that was not detected by Hunspell, I cannot tell them I use substandard Hunspell because Trados does not manage with Word spellcheck...

try this and let me know if it works for you!

try this solution, I think it worked well, at least until RWS finds a permanent solution for this issue.

I cannot delete the Normal.dotm, since there are many essential macros I cannot live without.

Then make a copy of it, delete it, set the spell checker up in Studio, and once done, replace the new one with the old copied Normal template. I am sure this will work inshallah. 

When I did this, non of my macros were lost at all, so that you can be assured.

Unfortunately, something is really wrong and this is beginning to be a very annoying issue! Sometimes, I am able to do as Sorin said, among other further checks and cleanups, but everytime I restart Studio, I have to do all of this again and sometimes it works and other times I get the same error message! I guess RWS has to arrange with Microsoft for this nightmare to be over!