I think that the most debilitating ideas behind notation/time signatures is that EVERYTHING can be noted in infinitely diverse ways...as much as everyone likes to spout 'there is only one way to note this phrase', they are wrong.
There is usually one standardized way to represent a musical passage, but never one way to represent a musical passage in standard notation.
Once you have that idea...that notation is an abstraction and not a unique representation of a musical idea...you can then look at the ways to represent a phrase.
Expecting notation to be a 'one for one' with no alternative notation representations derails many.
With that said, a 'bar' can contain as many counts as you wish...we tend to select the number of beats(the number at the top of the time signature) that 'complete' a musical phrase though this is not demanded by standard notation...just by its convention...and the bottom number in the signature says what note gets one beat.
Things become real fun when you start using artificial grouping concepts to resolve issues where the number of beats to a notation phrase becomes 'more diverse'...like jumping to a spreading of 3 notes where 2 would usually exist(such as with half note triplets..which have several ways to be noted)...but this can extend to relationships of any form...such as treating 5 'beats' as though they filled 7 'beats' (5:7 read as '5 to 7') as noted in the time sig.
In the end, I am not so sure that understanding this bit of theory is all that helpful in most situations outside of cold reading responsibilities..though it does give you mental exercise and a new 'toy' to play with.
i defer to the folks that went to the effort of attaining a deeper music theory education than i...as long as they do not violate the basics of logic! : )
....sort of like the English language....
there are rules. And then there are exceptions to the rules
there are foundational situations. And then there are variations on those situations
the key, at least for me, was making sure that I knew the foundations so I could prepare for the variations. I don't beleive that time signatures are as ambiguous as they are made out to be if the learning process is in the right "order"
I was lucky(?) that my dad taught me time signatures, and how they worked, right out of the gate when I was 4 years old. I don't ever remember a time in my musical life where I couldn't figure stuff out by counting and getting the time sig in my head.
4/4 - top number is pulses per measure; bottom is the kind of note that represents those pulses. If there is 4 in the bottom, the pulses are visually represented by quarter notes.
He also taught me the subdivision rule: a rhythmic value can be broken down into 2 smaller rhythmic values. That helped me understand how to put smaller divisions in between the pulse rhyrhms, hence, 8th notes and 16th notes.
I learned this stuff before he taught me any drum beat.
then, he made me learn Take 5 by Brubeck...but we started by counting along to the song. He made me learn the rhythm of the piano part first. once I could count that, then we started on the drum part - by count - and with the hands only. After that was good, I added the bass drum, and then the hi hat. Also during that time, he had explained to me what spang-a-lang was, but again, by way of counting.
granted, this was a months long process with a lot of failure at first...BUT...having this foundation allowed me to quickly learn other songs as I got older and wiser. It allowed me to be able to count the beats of a part out loud before physically learning it, which allowed the physical to happen much quicker. I think it also gave me a sense of control that helped me get over frustration with failure at first....like I would say "I know I can count this in my head...I can envision it. I just have to keep trying to get it to the physical of my limbs"
I also remember discovering that time sigs could "cross over"...like 3/4 and 6/8 and 4/4 and 12/8, round about 6th or 7th grade, when I first started working on triplet feel stuff in school band, and triplet feel songs like SATO by Ozzy, Where Eagles Dare by Maiden or The Whisper by Queensryche.
but I digress....I feel that if you take the time to dig into what time sigs are, they can be a great help...not a hinderance to playing beats!!!