I‘ve asked my previous employers to print out the reference letter and then send me a scan copy with signatures or company seals during lock downs/WFH period. For one employer who told me he had no access to a printer, I've uploaded the ref letter w/o signature, together with a LoE attached to explain the situation plus a statement that my employment can be verified thru email/phone number. It worked well during my provincial nomination period in 2020.
However, new guidance from IRCC may seek extensions for applicants to acquire supporting documents. Application maybe deemed incomplete for lacking necessary documents. Not sure if it is because the Covid card is being played too much.