Under ATCP 134.06 (4), (a) "[i]f any portion of a security deposit is withheld by a landlord, the landlord shall, within the time period and in the manner specified under sub. (2) [MEANING within the time to return the security deposit or 21 DAYS], deliver or mail to the tenant a written statement accounting for all amounts withheld. The statement shall describe each item of physical damages or other claim made against the security deposit, and the amount withheld as reasonable compensation for each item or claim.
(b) No landlord may intentionally misrepresent or falsify any claim against a security deposit, including the cost of repairs, or withhold any portion of a security deposit pursuant to an intentionally falsified claim."
Hence, the answer is that, yes, by not objecting to the damages within 21 days of you moving out, he waived the right to object. Moreover, if the damages are mere "wear and tear" or not something the tenant could reasonably be held responsible for under the law, he or she isn't liable to pay anyway. Whether this is mere wear and tear is unclear from the facts at hand. However, it very well might be. And, either way, by not objecting within the time to properly do so, the landlord has waived the right to object - through deducting from return of the full security deposit within 21 days from the time you moved out.
The answer to your question, is yes, if you damaged the apartment then you are liable for the damage regardless of if notified within the 21 day period. The question of whether you have actually damaged the apartment is uncertain as it does appear that some of the charges your landlord is claiming may be considered normal wear and tear. However, the question of liability is totally separate from the landlord's failure to provide written notice of the damages within 21 days. If a landlord does not return the security deposit or send a written document showing deductions, you are entitled to recover double the security deposit from the landlord.
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