Would you consider adding an SGLT2i for a patient with proteinuric kidney disease who is already on maximal dose ACEi/ARB and has a UACR < 300 mg/g?

I not only would consider it, I've done it on many occasions. There's nothing magical about UACR <300 that eliminates the risk of CKD progression. The risk decreases but it's not an inflexion point. The lower the albuminuria, the lower the risk of progression, which has been well demonstrated in IgA...

I offer SGLT2 inhibitors to CKD patients with GFR > 20 even in the absence of albuminuria. There is some renal protection benefit, perhaps not as robust as in proteinuric patients, so this aspect needs to be emphasized to the patient. Emerging real-world data support a renal benefit in non-diabetic,...

Yes, as long as the eGFR is > 20 (no data available for below 20).

I think we should up to UACR of <150 mg/g unless the eGFR is <20, in which case, it is likely to not help out much.