Can I contribute to spouse’s 403(b) myself? Ideally trying to do for 2025 & 2026 tax year and I’m assuming 2025 could be posttax contribution only.

My spouse has been only doing max contributions to her 403(b) plan despite my recommendations to ensure it’s max’ed out each year.

I’ve been doing a backdoor Roth each year for her instead but clearly not sufficient.

Can we do posttax contribution until I finally get this straightened out?

Background: Lincoln financial. And yes, salary is sufficient for ira/403b.