Cells and columns keep reformatting on their own

Can anyone advise me on this?

My cells don’t keep the formatting I set - the font changes, the alignment moves from left to right, and the currency column reverts to general number.

Is there any way to save or make default my selections so they don’t keep changing randomly? As I spend more time continually reformatting the columns and cells, than I do putting data in them…

Using Mac Big Sur. Thanks

An advise: start by making yourself understood. E.g., add something like this:

I use LibreOffice 3.3. When I open my CSV, that I edited yesterday, I see all the formatting lost.

Or:

I expect that when I set my styles, the new spreadsheets have the formatting I defined.

Or:

I press button X, and the format is applied; but if after that, I select menu Y, the format is immediately reverted.

… or whatever detail may help someone not looking over your shoulder, to understand what you mean. Thanks.

It sounds as if the document is saved as a txt or CSV file. Save as .ods which is the native format for Calc

Ernest AI nailed it,
Apologies for my poorly constructed sentences, bad English, frustration and concise description.

It’s: I’d advise, or My advice, or Some advice, not ‘An advise’.

Most people giving advice here have English as a second or third language. One might find similar difficulties translating into grammatically correct Russian.