What are the repercussions for not having a record ACFT for the year (if any)?

If you have a passing ACFT on record, then officially, 'not much'. As you aren't an NCO, you won't have an NCOER, but even then it's nothing more than showing you don't have a record one during the rating period and a note about why (temporary profile due to injury).

There are instances where there might be "repercussions" in specific situations (upcoming deployments, etc.), but you would have to specify what those situations might be.

The comments below are assuming that your profile accurately reflects your physical situation and that if/when it translates to a permanent profile you will still be unable to take the ACFT due to the limitations from your back and knees. If you ARE able to take the modified ACFT

However, there ARE possible repercussions regarding your comment of being "on temporary profile coming on 300 days now" that you should have been told about by your PCM and/or leadership:
• There is a term called the Medical Retention Determination Point (MRDP) that you should be aware of. In a nutshell, the MRDP is that point at which the military medical system says "we can't do anything more for them - either we can't figure out what's wrong or we can't fix it". Once a service member reaches the MRDP, it triggers a process to determine if that individual should be retained in the military or not.
• Military regulations dictate that temporary profiles in excess of 12 months are converted to a permanent profile (unless the first GO in your chain of command approves it after consulting with a few of senior medical and HQDA personnel) as it is the defacto MRDP point.
• If the permanent profile is a P3/P4, the service member cannot perform the basic soldiering skills required by all military personnel, or the service member cannot meet the specific medical requirements of their MOS, they will be referred to a MEB for evaluation and determination (AR 40-502*, para 3-3e).
• If your permanent profile does classify you as a P3/P4 in any area and the limitations imposed by your back and knees allow you to take a modified ACFT (you MUST be able to complete an aerobic event at a minimum), then you won't have any lasting impact (from the ACFT) other than taking a modified event in the future.

Suggest you read up on MRDPs so you aren't blindsided in two months with "SPC Hutchins, you appointment with the MEB is on Tuesday. What, you didn't know you were being sent to the MEB because of your back?"
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* AR 40-501 - Standards of Medical Fitness - https://armypubs.army.mil/epubs/DR_pubs/DR_a/ARN37720-AR_40-501-002-WEB-4.pdf
* AR 40-502 - Medical Readiness - https://armypubs.army.mil/epubs/DR_pubs/DR_a/ARN37126-AR_40-502-001-WEB-3.pdf

The only repercussions I can see is potential promotion since ACFT are a big deal now than before especially if you are in the Army National Guard as E-4 evals are no longer a thing as they used to when they counted for a lot of your promotion points. Lastly as the sir said, MEB for continued service.

Why haven't you had it converted to a permanent profile and gotten an exemption if necessary? I was on and off temp profile for my knee for a few months and in 2016 I got a permanent profile for it and then did the walk as an alternate (when it was APFT). When ACFT came about I did the rower (since there was no walk for awhile but I can row faster than I can walk now). Then I got exempted from the plank last year because of an abdominal muscle issue I have had plague me since 2012 and no one can figure it out.

If you can, get a permanent profile. At the bare minimum, with a permanent profile: "All permanent profiles must be updated by the Soldier’s medical provider to reflect the ACFT events permitted or prohibited. Soldiers must test on all events within the limits of their permanent profile. The minimum number of events a Soldier must take is one aerobic event (run, stationary bike, swim, row, or walk)."

I retired in Sept, my last ACFT was April 2023. I was due in October 2023 - but I had to get a temp profile for my back (and I was retiring anyway with terminal leave starting in June so I didn't care about taking one). My last NCOER (that I still don't know why they did - oh for someone's rater profile) I think there's a bullet you can put that says "SM was on profile" or something. I can't remember.

Seriously though look into a permanent profile. Then see what you can do on the ACFT.