I have a similar issue....Where is it possible to change the Invoice sequence format.  I would like it as follows: INV-YYMMxxxx, where xxxx resets every month.

I found where to change the sequence for purchase orders and sales orders, but the same method does not appear to be available for invoices (ie: the "sequence" doesn't seem to exist in the same place for invoices).

The closest I could get was INV/25/03/0005, where Odoo detected the year/month/number, but I can't find where the delimiters/format are defined.

Thanks in advance!

Since you don't want to reset the sequence to 1 for the next year, your actual sequence is F-xxxx.. the YYYY is just for cosmetic only and has no effect on the sequence. This is not an odoo problem, it's just you want something else that odoo is not designed to do and some customization will be needed.

I usually do it in code, but in your case, maybe you need two steps:
step 1: generate the sequence with just prefix F and it will just work
step 2: replace the reference from F to F-YYYY using some kind of automation.

However, since you already have data and the sequence for 2024 is already created. So maybe for 2025, you can change the sequencing to have next sequence id of the last sequence id of 2024+1 and hopefully it will work for the whole year. next year, you manually set the next sequence_id again.