I would suggest the Bro post be a separate post.
The "Unrecognized database format .... Database.accdb" seems to have become prevalent in edition 2019 / 365.
I've spent some time with it and there is Q/A on this topic here at this forum. this is in reference to the BE going into this state due to user activity - - and not where development has been done in a newer edition - which is an entirely different issue.
My observations are:
a. mostly seen in older apps that were originally .mdb format but now .accdb / one of the suggested fixes, that did work for me in one situation: change the BE file back to .mdb
b. the FE design must avoid having the same table open in edit mode, at the same time. If 2 forms both source on Table 1, in an editable function, both forms should not be open at the same time.
c. strict adherence to a primary key in every table. and careful review of any look-up table/field properties being used.
