Textra: getting rid of ancient, unwanted messages which Textra refuses to delete?

I've been using Textra for many years. I'm currently on Textra version 4.80 under Android 14. I recently learned that Textra keeps its own internal database of SMS and MMS messages and uses that in conjunction with the Android device's message-storage database ... and possibly even instead of the device's message-storage database. I have set Textra to keep only 25 SMS for each conversation and only 10 MMS for each conversation. This ends up being a total of a bit more than 400 messages total. And I have specified numerous times that Textra delete extra message storage, which Textra always says is successful. However ... when I examine my device's SMS/MMS actual message storage, there are several tens of thousands of messages being kept, most of them being very ancient. I want to totally and completely and permanently get rid of all SMS messages that are older than 25 per conversation and all MMS messages that are older than 10 per conversation. I have used Textra's "Resync Textra" function, and it does not get rid of any of those tens of thousands of ancient messages. All other SMS apps still see all of this huge quantity of messages. And if I ever change the SMS app, I want all other Android SMS apps to not see tens of thousands of ancient messages in the SMS/MMS database which I am trying to delete, and to only recognize the 400-or-so messages that I want to keep. How can I clean up my SMS/MMS message storage so that only the 400 or so messages remain for Textra and for all other SMS apps, with all of the other older messages being totally and permanently deleted? **UPDATE**: It's important to me to use an SMS client which allows me to also record and send and receive voice messages directly from the message client (not voice-to-text). As far as I know, Textra and Google Messages are the only clients which allow this. And Google Messages does not offer the deletion-of-old-messages function that Textra offers (I'm talking about the deletion-of-more-than-25-SMS-and-10-MMS-per-conversation that I mentioned above). Therefore, my options for switching to something other than Textra seem to be quite limited. **NOTE**: I got rid of the "Further Update" section that I had previously written here, because now I solved this problem in the "Answer", below.