Hardly anyone enunciates the 'x' in a word like 'sixth'. I say 'sikth' (and I fancy myself a fairly eloquent speaker). It's got too many consonant sounds; the human tongue just isn't agile enough for a word like that. You might get it properly-enunciated by a university don, or certain kinds of very pernickety radio presenters.
YMMV
Specifically Gutenburg and his hellish press. Before movable type English had the letter “thorn” - perhaps some of the pronunciation problems arose then?
But what do I know? As a nativ spanich spikr, I rimembr bing prplexd
Random related anecdote: For years the Mormons would distribute their Book of Mormon in German translations but these were printed overseas and they didn't have the 'ß' character, so they used the greek letter β to substitute 'daβ' instead of 'daß', etc. We tend to forget living in the digital publishing age how limiting mechanical workflows can be.
This β <-> ß confusion endured into the digital age.
For example code page 850 has a character called "Sharp s Small" but it is placed among Greek characters. And several fonts didn't display an ß but a β https://en.wikipedia.org/wiki/Code_page_437#cite_ref-21
In this case, the double use was probably intentional (to save space in the limited character set range) but still confusing to the reader when they encountered the wrong glyph.
https://historyofenglishpodcast.com/2016/12/07/episode-87-th...
Though and tough aren't a problem though, "thinking" in the middle of a sentence is real tough though.
2. Let out all the air out until your tongue separates said teeth