RTC filter transfer to Classic Report

If the number of records is limited and the primary key is a single field, then there is a simple solution.
Build a filter for the primary key like this "<primary key1>|<primary key2>|.."
(Please ensure the primary key field doesn't contain any special filter chars: &, *, |, (, ), ?)

Otherwise I guess you will need to press the magic button "Create Layout Suggestion" [-o<

Another thing you could try is to insert the records you want into a temporary table variable in the report, instead of pass the marked recordset. (You can set the record to be a temporary table be setting the property temporary = yes.) A new function in the report can be used to insert the records you want from the codeunit into the temp table. For example, your function in the report could be:

InsertRecords(Lot : Record "Lot No. Information")
tmpLot := Lot;
tmpLot.INSERT;

You can then call this function from your codeunit to insert the marked records. The below uses a report variable to call the function created above.

// Lot filtered for marked only already
IF Lot.FINDSET THEN
REPEAT
myreport.InsertRecords(Lot)
UNTIL Lot.NEXT = 0;

In your report you can now use this temp table to loop through the records. With dataitem of type Integer you can use something like the following to go through the records:

Integer - OnPreDataItem()
SETRANGE(Number,1,tmpLot.COUNT);

Integer - OnAfterGetRecord()
IF Number = 1 THEN
tmpLot.FINDFIRST
ELSE
tmpLot.NEXT;

All the table fields in the report need to point to the tmpLot table, and the data will be shown as normal.

Lastly, you need to run the report from the codeunit using the report variable:

myreport.RUNMODAL;