After some year of use, I would like to delete older transactions: maybe all transactions before a given date, typically an end-of-year. Investments that remain with no transactions at all, may be deleted with all its prices, as a consequence of deleting transactions. More complex but with some advantage, delete old transactions only in user-selected accounts.
I would strongly argue that you really don't want to simply delete old transactions, but to "archive" them in some manner, so they are not displayed and do not slow down any current operations, but are somehow available should you have need to check them. There is already a bug for this "end of year reconciliation and archive of old transactions" (with a better and shorter description, I think, but I can't find it right now.) One reason, for example, you might not want to delete old investment transactions without special handling is that the information is necessary for performance reports, and to know the basis (original price paid) when you sell. While KMM doesn't handle that type of thing now (capital gains) there is also a wish list to add it.
Thank you for your comment, Jack. As you did, I tried but I couldn't find another proposal for "archiving" old transactions in KMyMoney. Yes, you're right, investment transactions cannot be deleted so simply. Nevertheless, at the moment KMyMoney does not retain independent memory of the investment purchase price, for setting revenues in investment selling. I understand that it is very difficult to take into account the various ways to conserve purchase prices - LIFO (FIFO?) lots, or average purchase prices. But, IMHO, for reporting purposes, it is inaugh to conserve the last price of investment before at the end-of-year date. Obviously, only when we want delete old investmente transactions. About deleting vs archiving / "freezing" old transactions, I'll prefer deleting, as the KMyMoney file can be copied, protected and archived with OS facilities. Thank you for attention Jack!
Adding "see also" as it's not quite a duplicate, but does seem related.
https://forum.kde.org/viewtopic.php?f=69&t=173061&sid=efbb7f1165b7070b376cc9ad26706b7d#p449929 contains some information how to obtain this behavior in a manual fashion. Not so much on the investment side of things, though.