I do not have a choice of wotlk (old) expansion

I wanted to return to the game after a longer break and after pressing the doownload tab, the option to select the wotlk (old) does not appear

The launcher with automatically placed new models was removed due to issues it had. You must download old launcher and manually upgrade the models using some of the guides on the forum that were "confirmed" here or head over to Technical Guides and look through the unconfirmed guides and models.

I mean, I only see Wrath of the lich king and Mists of pandaria and is this WOTLK version 3.3.5a?

It were Old models and Legion models, not expansions like 3.0.2, 3.1 etc. So logicaly, if updated models client was removed, it is obvious that there is only 1 actual client left